Upgraded KS P90 = $445
I'm just getting my first gun after being on here for a year almost.
Don't forget about everything else like the loadout, etc. That could be just as expensive.
My advice, the cheapest good quality gun I can think of that comes to mind is priced usually at $300 plus shipping.
You can also cheapout and get cheap Sig 552's, I saw two people had at Green Zone, but you stand out alot if it isn't painted and performs low.
This hobby isn't cheap sadly if you lived in asia though, that would be a different story