[L473ncy]

I'd say $500 will get you nicely setup:

King Arms M4 Rifle ~$275-300 shipped (just use the stock hi-cap for now if you don't have too much money)
Battery, charger, BB's etc. ~$70 (Get 7.4V lipos from Hobby King and a charger like the Imax B6, and buy Green Devil, BBBastard, or Madbull BB's or whatever is available to you)
Surplus CF Olive BDU's ~$70 set (trousers, tunic, field cap)
Good boots if you don't have $100-150 (can use hiking boots in a pinch and I've played in my hiking boots for 3 years but recently got a pair of Magnum's)
Eyepro: You'll already have this if you come from paintball, a set of JT Spectras or Flex8's are good so you can take off sections to get a good cheekweld and use your sights
That's pretty much all you need to start out. After that you can pickup chestrigs or vests and midcap mags and whatever the hell you want or think is cool.