Can anyone give us an idea, We are heading to German from Russia in august and are planning a drive in Europe no time limit. two of my friends and me, how much a camper van for 4 persons would cost in German. can we buy from anywhere (or good place to buy it ) , Any help will be good

I would avoid buying in Germany as prices tend to be higher. Plus I don't know what kind of issues you would have with registration, insurance, and TÜV inspection.

As for prices, here are some: http://www.mobile.de/wohnmobil-verze...westfalia.html

Buying and reselling is not practical. Not only do you have a high upfront have to get one in decent condition? How much will you have to put into it to keep it running? How will you get insurance without a driving history (for each driver)and a fixed address?? And how long will it take you to sell it once you are ready to leave? And at what price?

That said, if you are from Russia how long are you allowed to stay in Schengen on a tourist visa?

It would seem like renting is a much better idea.

Firstly if you are Russian citizens you will need Schengen visas.
You will not be able to insure a vehicle without a permanent address in the country in which the vehicle is registered. No insurance makes the vehicle illegal.
Campers are expensive to buy, especially ones big enough to sleep 4adults.
Assuming you can get visas for such a trip have a search for a couple of Dutch companies who will sell you a camper, but will retained the title and insure it for you. They will then buy it back when you leave.
Make sure your driving licence is valid for the size of camper you want to drive.

Here is one such place, but there are others. http://happy-camper.eu/en/rv-rent-europe.html

These are more affordable. http://dutchcampervans.com/

BUT you must get visas sorted asap.