Eastern Europe can still be very cheap, at least compared to Western Europe. It is still possible to do Prague on $20 a day, but nowadays that will be good enough for a large dorm room and eating street food or food from markets. If you increase your budget to $40-$50 a day you will be able to have a more luxurious time (eating out, a few drinks, sights, smaller hostel room). Budapest I actually found a little more expensive than Prague, but I did tend to splurge more in that city than probably necessary. Poland is cheaper than Hungary and Czech Republic. Even in Krakow and Warsaw, $30 a day will be sufficient enough funds to cover a room, eating out once, having a few drinks and seeing a sight or two.
It all depends on what you are looking for in the East. If you are looking at eating big meals at restaurants, going out to clubs, and the like, you can do it for cheaper than Western Europe, but you are not going to be able to do it on $20 a day like you might have been able to ten years ago.