Still reasonably cheap by British standards, but very much more expensive (and to my mind, less attractive) than it was when I worked there a few years ago. Joining the EU and becoming host to numerous stag & hen weekends have done absolutely nothing to improve Prague's charm. Having said that, it's still a beautiful, interesting city with plenty to see and do - I can't agree with Fish that a long weekend is enough; I spent over a year there and go back at least once a year to see friends, and I still haven't seen all there is to see.
Hotels in the city centre have always been, and still are, overpriced; go for somewhere just outside the centre - public transport is easy, safe and extremely cheap - and you'll do much better. Same goes for food - it's generally very good, and you don't have to go far out of the centre for prices to fall dramatically. You'll have to see Wenceslas Square, Staromestske Namesti and Karlova once - but once is enough, and you can only take so much overpriced tourist tat. Mala Strana is much better - still not over-commercialised - and the bars and restaurants round Betlemska are second to none. Enjoy my favourite city (after my native Birmingham, of course!).