The BBC spent almost £700,000 on its anniversary half-hour live episode of EastEnders last year, a new report has revealed.
Corporation bosses earmarked an extra half a million pounds - over and above normal costs - to fund the 25th anniversary programme.
The figures are revealed in a report by the National Audit Office (NAO) into the way the BBC manages the costs of continuing drama, which also shows the Walford soap will spend nearly £7 million on cast this year.
It found the cost of six key dramas, including EastEnders and Casualty, has reduced by a fifth in real terms over the past eight years.
However with audiences declining, the NAO study also found the cost per viewer for the six programmes had actually risen by almost 9% in real terms over the same period.
The NAO concluded a lack of formal objectives for the dramas meant it was unable to say whether the BBC was actually delivering good value.
But it said the corporation had taken "important steps" towards achieving value for money with its cost-savings.
The NAO looked into UK-wide shows Casualty, Doctors, EastEnders and Holby City, plus the Scotland-only series River City and Wales's Pobol y Cwm which cost a total of £102.5 million in 2009/10.
The report details how the cost per viewer for EastEnders is a third of that for Casualty.
The hospital drama is the most expensive drama in the report at 9.4p per viewer, while EastEnders - the cheapest - costs just 3.5p.
Albert Square's live episode cost a total of £696,000 the NAO report showed, which included the extra £500,000 to fund expenses such as extra cast and outside broadcast facilities.
It proved to be a huge audience hit with 16.6 million watching on BBC1 in February of last year, and it was the most-watched drama of the year. A BBC3 spin-off straight after set a new record for a digital audience in the UK.
A live episode of ITV1's Coronation Street last year, to mark the soap's 50th birthday, is said to have cost up to £1 million - although that did involve staging a tram disaster, with large sections of the set in rubble, plus CGI effects.
A request to find out the cost of the EastEnders episode under Freedom Of Information legislation had previously been rejected.
Two-fifths of the cost of the live episode - which represents the standard cost of an episode - came from the show's £29.9 million budget for 2009-10.
Figures in the report show the EastEnders overall budget has been reduced by £6 million from six years earlier, although it is still the largest of the six shows under consideration.
The report reveals EastEnders will spend £6.9 million on cast this year with a further £2.6 million on scriptwriters and story advisors, which accounts for 32% of the budget - the same proportion as the previous year.
Amyas Morse, head of the NAO, said: "The BBC is doing a good job of applying basic financial controls and achieving steady cost reduction across its portfolio of continuing dramas.
"However, it should take a more holistic approach and compare the cost of these programmes with audience levels and opinions, both targeted and achieved, as these are critical measures of broadcast performance, and a key guide to whether the continuing dramas are delivering value for money."
BBC1 controller Danny Cohen said: "Continuing drama on BBC1 delivers high-quality British programmes that reach huge and appreciative audiences.
"Today's NAO report shows costs have dropped by 20% but at the same time, audience appreciation has risen considerably. On this basis, it provides excellent value for money for licence fee payers across the UK."
The BBC Trust said it was pleased with the finding of a 20% real terms reduction in costs.
Trustee Anthony Fry, who is responsible for value for money, said: "The report shows the BBC has made real progress in delivering value for licence fee payers, an excellent achievement of which the BBC can feel proud.
"Popular, long-running dramas like EastEnders sit at the heart of the BBC schedule, generating loyalty from audiences as well as an environment for new writing, acting and production talent to flourish. They cost viewers less than they did 10 years ago, while audience approval is on the up."