I've just been to prague but we are very frugal and hardly spent anything. we hired a gorgeous apartment for 5 nights for £206 which included a cooker, washing machine and dishwasher, so I cooked all our food. There is a tesco and plenty of Billa, Albert and DM supermarkets. We also bought 500ml bottles of beer in the supermarket ranging from 6kc ( 20p) to 20kc ( 70p) if you have a boat ride, go and see the little stall by the river behind the bridge ( walk over Charles bridge, take a right once under the arch and follow road round, past a pub, until you get to grassed area. Its actully also once you go across that field, over the road from metro malastrana, and theres a water fountain there to fill your drinks up ) they charge 250kc, but tell them the lady that came for her silver wedding sent you to them and they will do it for 200 each, you wont find cheaper. transport tickets are really cheap, 110kc ( less than £4 )each for one day or 330kc each for 3 days and the good thing is they last 24 hrs after validating, unlike other cities which are only valid until midnight that day no matter when you buy them. (make sure you validate them the first time you use transport ) You can use them toget to and from the airport. depending on where you are this will take between 30 and 60 minutes. Must visits are Vysehrad. Absolutely beautiful and our teenage kids loved the Gorlice. Only 60kc each to go in and the man gives a fab tour of underground tunnels. The funicular railway up to petrin ( free with your transport ticket but then pay if you want to go up to tower etc or just wander round) If you change money use the big blue xchange shop on the corner in the old
town. You will know it as it has a big queue, as it gives a good rate ( around 280kc per pound. Ask before changing as some rip you off and will offer 190 - 250! Sorry cant offer any advice on eating out etc. But you will have an amazing time. We ran round like mad and saw so many sights! So many things are free. You will be lucky that the astronomical clock is back and working, it was being restored when we went

We were in Prague in February and I didn't find it as cheap as I was led to believe,
First of all be careful of taxis and make sure they have their meters on. We arrived at the train station, got an approved taxi who told us it was 20 Euros to out hotel. We thought that must be fair enough as it was an approved taxi (there are signs telling you not to use others) but we could have walked there in 10 minutes and did so on the way back.
Eating and drinking out? Can be expensive or cheap depending on where you go. Spent a fortune on a bottle of wine in a very ordinary place just of Wenceslas Square. Had similar in a beautiful place just near the opera house for much less. Art Nouveau Municipal Building is amazing. There is a cafe, a five star restaurant and a downstairs restaurant and bar. Five star restaurant is obviously expensive but the others are very reasonable. We wandered a bit off the beaten track (but not too far) and found some really great places where the locals eat.
I think what I'm saying is Prague is lovely but be careful and check the prices before you go in.