Prague is still pretty cheap, certainly as compared to the UK.
Last year I was paying between 20 and 70 kroner for a pint of beer. The first at a small neighbourhood place in the suburbs (I was visiting a friend) and the second in the old town.
Again, meals ranged from around 200 to 400 kroner for two, depending on where we were. You could certainly pay more and if you are going to eat mainly in the centre you'd probably need to reckon 300k a head on average for dinner.
A lot of Czech restaurants / pubs have websites with priced menus. If you google "czech restaurant menu" you get a range. You can then see the sort of place you fancy and the prices. Probably worth noting that a lot of the cheaper places don't run to a website,so you'll be looking at the top end of the price range.