Have you considered airsoft or reballing? I used to play airsoft, never played paintball. The land/playing area would usually be provided by someone one of the players knew, private forests, empty barns, junk lots, etc. We all had our own guns. We usually managed to scrape together 5-10 people for our games. Not sure about 100. That sounds rather ambitious for a game(?)

The general trick to owning expensive equipment is to find something with very little depreciation (usually top quality items) and buy used. This makes the carrying cost rather low. For example, my hand planes for woodworking are $300+ each, but I could sell them again for 90%+ of what I paid for them, so my effective cost is only thirty bucks. A brief search on the net reveals one can get 2000 paintballs for $30. Now I don't know if they're any good or not, but that sounds pretty cheap to me. How many shots for a game? 100? That's less than two bucks.

So I think you could do it pretty cheaply if you "invest" the money and do the organizing footwork.