The minimum amount of money you can deposit on romanian sites is 40 RON, that means about 10 $, witch is a reasonable amount. You can easily deposit with yours cards, phone or electronic money, whatever you want.
Be aware about yours withdrawal. The amount of money you withdraw, must be declared to the tax bodies, and pay the proper taxes in conformity with the winnings. If don't do that you will figure as a debtor to Romanian State.