Haven't rented in those specific countries, but here in Lithuania you can usually get a cheap car (and driver, sometimes) if you wait til you're in country and go through a local agency. Also, check www.inyourpocket.com
, to see if they have city or country guides for the places you want to go. (I know they cover a couple of cities in Poland, and I'm pretty sure Prague. Don't know about the others.) The website is pretty extensive, but the books are a treasury of info - usually cost about $2 in country, more through the website, I'm sure.