Hey there. Since I'm a Polish I can give you some advices in here. Eastern Poland is great place for people loving nature. On north east of Poland you should visit Mazury region. It consist with lakes and forests. During season, which is June September there are camper spots in almost every city and village. You can do: all water sports, bike riding, forests walking, hunting, fishing, mushrooms picking (late July September). Besides that you can visit Hitler bunkers where Operation Valkyrie took place (movie: Valkyrie, with Tom Cruise) if you like history. If you like to see very old forest (500 year old trees), and the European bison, which is the heaviest surviving wild land animal in Europe you should go to Bialowieza forest.
When you finish your lake/forest part you can drive south to Bieszczady mountains. These are not tall mountains with beautiful views, friendly people, very nice nature. Absolutely no industry. Im not so big fan of mountains, so I cannot tell you more, but you should google for pictures typing in the name.
In Poland it is not allowed to camp on public places, so you have to find a place.
4 Polish Zloty = 1 USD
Avarage prices per one day
Adult person 15zł
Child (2-15 years) 10zł
Camper 22zł
Trailer 20zł
Electricity 12zł
Pet 5zł
So two adults with camper, electricity and pet = around 17 USD.
Additional information:
Gas prices are much higher in Europe, then in US.
Food, specially in a grocery shops are quite low in Poland, comparing to other European countries.
Polish people are friendly to Americans which is not always the case.
Polish old people dont speak English they speak Russian.
Polish young people can speak English, at least they understand, so you can use your hands to sort things out :).
Poland is very safe country.
From Mazury region you can drive to Lithuania. I have a friend there, if you need advices from there. From Bieszczady you can drive to Slovakia within 1 hour I have a friend there too, so I can ask him too.
If you need anything else, please let me know. If you decide to came definitely let me know! :)
Best regards
Teksanski