You have to factor in about $100 for a battery and charger (BB Bastard)
About $50 for a couple bags of BBs (BB Bastard)
About $50 for a high cap
That leaves you with $400. You best get verified and buy used. Or go for a MP5K, etc.
I will assume that you already have paintball goggles and will be ok in some dark clothes you found in the closet.