I STARTED with ~$550-600 in but note that that's just the initial investment. After about a year I would say I was closer to $750-900 in.
I assume you're 18 now.... and if you just wait until you can meet an AV rep to get verified you will have a larger selection of guns to choose from. $450 for a decent gun with 2 or 3 mags and maybe a cheap red dot is a reasonable price to pay. After that $30-40 olive drab combats from the local surplus store, $40 paintball mask (or if your field allows it fully sealed ballistic goggles or just shooting glasses), boots (I assume you have otherwise winters would just suck) but perferably if they're in an "earthy" brown, tan, or black colour that's great (ie. don't come to the field wearing something like this
something like this is better
notice how the first is blue and has reflective stripes whereas the second one is in a neutral grey tone).
I guess when starting out a mag can go in your BDU pocket (and even I'm considering doing that when I do a lightweight loadout) but you can always borrow a vest if anyone has a second one or whatever. Also I say it's fine to use a hi-cap mag for your first 2 or 3 games but after that they're not expensive (especially if you go with an AK or AR15 platform since you can get STAR or Magpul "Green Label" which end up being like $8-9 a mag and come in boxes of 10 so you could split with a friend if needed)