depending on the play style and how seriously you guys play, a decent basic package (in my opinion for someone getting into the sport at least) is a g&g raider (comes with one high cap mag) thats about 200$, a battery usually goes for anywhere from 10$-80$ depending on nimh/nicad/lipo and voltage and mah. A paintball mask will do the trick. they can be had for about 40$ and bbs about 20-30$. go to an army surplus store, pick up a set of bdu's or even some form of camo style clothing you may have already.
thats just the absolute minimum
mk43, ump.45, p90, barret, m14, g33, k98, m4 tac, m4 swat, mp5 navy, vsr10, p226, m9.