A YEAR after the deregulation of television listings, the market for programme magazines is proving highly price-sensitive. In the Audit Bureau of Circulation's figures for the first half of this year the biggest gainer is IPC's What's On TV with a weekly sale of 1,401,031, up by 93.8 per cent compared with a year ago. At 33p, it is the cheapest title. Its up-market sister, TV Times, costing 55p, sees sales well down at 1,109,359. What's On TV could soon vie for market leadership with BBC Enterprises' Radio Times, which averaged 1,562,770 and has just gone up to 60p. Bauer's TV Quick (43p) has not yet published its figures, but they are expected to be between 650,000 and 700,000.