the idea of ruining the game - you have an option to hit the store before entering the server and buy ammo, weapons and night vision for real money. Mwahahaha!
Thats a terrible idea. a somewhat less terrible idea would be to have some kind of barter system where you could trade the items you have for other items. So if you want a map, you can trade in your morphine and an ammo clip.
Still pretty terrible, but it would at least provide a risk/reward and be based upon the actual game and no any kind of artificial monetary system or disgusting micro transaction of real money.