My experience has been a bit different. I have a friend who pretty heavy into airsoft, so he's been lending me guns and vests to use when I've played. Good guy that Nacchi is
So my expenditures were:
JT Paintball mask: $25 - (got it at Walmart, it was out of box and no price tag, I talked them down to a deal)
Gloves: $5 - USMC gloves from LeBaron
BDU & Boonie: $180ish - Propper Multicam from bdu.com (MC is a more expensive BDU to buy than most, as people have mentioned)
Boots: $40 - Used tan boots from Army Issue Surplus
Total: $250
I've since bought Oakley knock-off's and a hydration pack from ebaybanned, but you can get by without both of those.
If you do know someone in your area that is willing to lend or rent you a gun I would suggest it, especially for your first game or two. First of all it may give you a chance to check out a couple different types of guns. Second, you may not enjoy airsoft as much as you think you will (though I doubt that!). In terms of mags, I've never used a hicap, but I like having to reload under fire, much more exciting
A lot of people say you should get 10 mags, but personally I haven't shot all that much, maybe 3 or 4 realcaps at most without dying (as a newbie you'll probably be doing a lot of that, like me!) and you can usually reload your mags at your respawn anyway, so you can save a few bucks by not getting quite as many mags for now in my opinion.