Some tips for you. First off you don't need the high end gear made for paintball a lot of the time.
Clothing- I started out with camo from thrift shops, and jeans work great too.
Depending on how much you shoot during a game, you can pick up a 2 pod holder with pods at wal-mart pretty cheap.
a lot of things like sights and optics for real steel work on paintball as well, so if you have some laying around, there you go.
A bunch of us here have been known to mod things for our use, I once took a cell phone case and turned it into a mag pouch for my pistol.
As far as old paint, I would use it for practice but not games, the reason for this is old paint gets sweaty, brittle, dimpled, these things can make you paint go in wild directions.
You can also check out the B/S/T threads on some forums, and there is a milsim B/S/T on facebook that has some good deals at times. here it is
https://www.facebook.com/groups/MilsimBST/I always keep my eyes out for deals in all kinds of places, yard sales, thrift shops, and things that I can mod for my use in paintball.
Hope this helps.
