The same is true of new numbers, says the magazine Comics International. The first issue of the oddly titled US publication Coventry proved so popular that copies were changing hands at a tenner each until its publishers shipped over fresh supplies, whereupon the price fell to the one on the cover.
A further tip from Gravett: when buying the first edition of a British comic, make sure that it's still got the free - yes free! - gift often attached as a lure for young readers.
You don't need X-ray vision to realise that comic collecting is a serious business. Superman alone takes up eight close-packed pages of The Comic Book Price Guide, including as it does the 1942 number with Hirohito and Hitler on the cover, as well as Superman: The Secret Years and Superman: The Wedding Album. "Superman: The Bankrupt Collector" would be the likely fate of a "completist" who craves long runs from the early years of this brand-leading title.
Cartoon strips have come a long way - out of the newsagent's and on to websites. They have inspired Pop artists. (When the late Roy Lichtenstein drew speech bubbles, it counted as art; when DC Comics does it, it counts as artwork.) Collector's guides are heavy enough to rupture the Incredible Hulk and collector's fairs - there are regular ones at the Royal National Hotel Holborn - are as packed as the dungeons after Judge Dredd has been on courtroom duty. Some of the prices are cosmic too. Ownership of issue No 27 of Detective Comics (DC), in which Batman made his debut in 1939, prior to his popularity securing him his own title a year later, would involve extracting pounds 100,000 from your Bat-wallet. The same sum would cover the first appearance of Superman, in Action Comics No 1, dated June 1938. In fact, a copy is said to have been offered for sale in the USA at a quarter of a million dollars.
Superman, of course, hails from the other side of the Universe - and of the Atlantic. But British comic strippers can also hold their heads high in any part of the galaxy, if Gravett has his way: "Our aim is to set up a Museum of Cartoons. There is a lot to celebrate in British cartoon art - from William Hogarth to Judge Dredd." The Trust presents cartoon awards and also puts on one of the few fairs specialising in British art. In addition, it organises evening courses and children's workshops for the next generation of cartoon strip teasers.
The Trust would also like to see members of the older generation receive due credit when their (back) number is finally up: "When Herge died, Tintin images were used instead of photographs throughout an entire issue of the French newspaper Liberation."
"When the creator of the Italian adventure hero Corto Maltese died, he made the front page of Le Monde," adds Fiona Jerome, editor of Bizarre magazine and a contributor to the latest The Slings & Arrows Comic Guide. This covers largely American, European and "manga" (Japanese violence, loosely translates as "irresponsible drawing"). It includes no prices but its criticism packs a punch - the entry for Green Goblin sneers "Pass the barf bag" - and it ranges from the usual superhero suspects to out- of-the-way material such as I Saw It by a survivor of Hiroshima.
Fiona has been a reader and collector - in that order - for over half her life: "When I started 17 years ago, there were only a handful but now most towns have their specialised comic shops. You will find boxes with comics for as little as 10p or 20p each." On the other hand, anyone who wants a decent run of classic numbers should set aside thousands of pounds.
"The Forties and early Fifties count as the 'Golden Age' of comics," she says. The "Silver Age" covers the mid-Fifties to mid-Sixties, while the "Bronze Age" runs from the mid-Sixties to the present. A Batman can cost several thousands from the Golden Age but a fiver if it dates from the Bronze. A lesser character from a recent vintage might be a mere 50p. "It also depends on condition," Fiona says. The value of an item can vary from pounds 500 to pounds 15,000.
"Comic collectors are fundamentally anal," Fiona Jerome admits cheerfully. "Some won't let you see anything without washing your hands and they keep their comics in temperature-controlled, light-controlled vaults. Some get hyper about it. But a lot are casual, like me; I just buy, read - and don't throw away. I put them in bookshelves and don't leave the windows open in winter."
Some adults justify their hobby by declaring that it is all for their kids, but this brings a new terror: "How do they stop their children spoiling their comics?" wonders Fiona. "I've known collectors buy two copies."
That advice is far too late for a colleague who had lovingly preserved a copy of Eagle from his childhood - only to have his little boy snip out and post a coupon for a bicycle which had gone out of production three decades earlier.
It is typical that the over-enthusiastic child with the scissors was his son rather than his daughter. Although early examples appealed to both sexes - Larks! came out in 1893, while The Sunday Fairy and Merry Moments were two of the titles in the comic explosion of 1919 that followed the end of WWI - more recent titles gender specific. Girls have tended to jump from Twinkle, about dollies and ponies, to pop publications. And females traditionally make up only a fraction of the clientele at comic fairs.
"Huge, muscular heroes and large-busted women appeal largely to adolescent males. It's only in the last 10 years that people have started comics about being young and female," says Fiona.
It was a boys' own zone when Denis Gifford began reading, and then drawing, for comics. He is a former artist whose penmanship included the cartoonisation of "The Adventures of Baron Munchausen" in the long gone Classics Illustrated series (now worth pounds 20 in Britain and $100 in the USA). He was also one of the artists who, each week, would share the work on Marvelman, the UK answer to the USA's Captain Marvel; copies of this 32-page comic then cost 6d (2.5p) and today fetch at least a fiver.
Now he is a writer whose books have included The Complete Catalogue of British Comics, which he compiled 20 years ago. Gifford sees the collector of British comics as being a man in his mid-to-late thirties, rooted in nostalgia: "When he's buying comics for his kids, he then starts buying the comics of his childhood." If he's in luck, and not too particular, he may have to pay less for his nostalgic items than for his children's: "For a Topper or Beezer, 50p to pounds 1 would be a high price."
Even the fledgling issue of the weekly which launched Dan Dare will not cause a black hole in the bank account: "Eagle No 1 would cost between pounds 10 and pounds 200, depending on condition." One of the quirks of the market is that, in order to make the most massive impact, the launch issue had a vast print run; issue number two, with its more modest total of copies, is now actually more scarce but worth not much more than a fiver. Gifford reckons that other early issues can be picked up for as little as pounds 1.50, slightly more for the Christmas specials.
All comics brought out their Christmas numbers and young Master Gifford would snap them up: "I loved the way snow used to hang over the title on the front page and the last page was always a Christmas party. And there were bunches of holly in the corners of the pictures."
For some of the old comics, there are invisible pound signs lurking too. While Eagle wasn't hatched by Rev Marcus Morris until 1950, DC Thomson's long-lasting Dandy and Beano, which began in 1937 and 1938 respectively, are now bubbling along nicely as investments.
"The first issues have fetched over pounds 4,000 each!" declares Gifford. You can practically see the exclamation mark hanging over his head. Even 20 years ago, when he was compiling his catalogue, Dandy No 1 was valued at a mere pounds 25.
His attitude towards cartoon inflation, summed up as "GRRR!", is understandable - he tries to collect first issues, from yellowing veterans to the brand new comics. Intriguingly, he also collects final issues, which can be tricky to identify since the afflicted comics did not always admit they were heading for the Great Back Numbers Department in the Sky.
One of the difficulties of collecting British comics is that although they may be cheap when discovered in a box of back numbers, they are hard to find at comic fairs and specialist shops. Mail order is often a more likely source.
"The majority of our material is American," says Josh Palmano of Gosh!, the comic shop opposite the British Museum. This reflects the fact that British comics are not usually designed to be read after childhood, while their US counterparts cater for an adult or late teen market. Unfortunately it is as true for enthusiasts of DC Comics as it is for collectors of Dickens: whenever you decide to start, it is generally too late. The real bargains have gone.
In the introduction to The Comic Book Price Guide, Duncan McAlpine celebrates the single issue which set him off: "At the beginning of 1974 I bought a copy of Batman No 254 from my local newsagents ... From then on I started collecting Golden Age comics (mostly Batman) seriously." Those were the days when early copies could be found for between pounds 5 and pounds 50 and young Duncan managed to find a decent run from No 30 onwards. Today, he regrets, "The Golden Age of Batman is beyond the pockets of most collectors, which is a crying shame." His advice to newcomers to Gotham City is: "Collect what you most like and can afford."
As his Dreddship would bear witness, Paul Gravett stands guilty of the prevailing sin of the comic collector: over- enthusiasm. Of the 4,000 issues which he stores in his mother's home, many are not worth the storage space. Now he has to downsize: "My mother's moving."
He could certainly get rid of all those barf-making Green Goblins, for a start.
Cartoon Art Trust,67-68 Hatton Garden London EC1N 8JY, 0171 405 4717. www. cartoonet.net is a contact point for organisations. 'The Comic Book Price Guide' (pounds 14.99, Titan) 'The Slings & Arrows Comic Guide' (Aurum Press, pounds 16.95). 'Comics International' (95p monthly) 8 Trinity Rd, London N2 8JJ. Forbidden Planet, 71 New Oxford St, London WC1A 1DG, 0171 836 4179; mail order available. Gosh!, 39 Great Russell St, London WC1B 3PH, 0171 636 1011.