Expansion on the previous point: I bounce around national cuisines quite a bit, because I'm a cook as a hobby, and whilst, say, a gumbo won't cost you mutch if you're regularly cooking Louisiana staples, cooking it ab initio from a cupboard that's normally cooking Italian-influenced meals will cost you a small fortune. A quick look at my Louisiana recipe book tells me I'd need to aquire cayenee, paprika, garlic salt, onion salt, white pepper, spiced sausage, Tabasco (specifically Tabasco) and a bunch of other stuff. Then you need to get in all the meat and veg, some of which may be difficult to aquire from local shops or require specialist outlets, which adds in travelling time and cost, and which you'll probably be paying for higher quality for - at least if you're serious about cooking and food - than you might for a common-or-garden meal. That makes your one gumbo cost almost as much as it would at a restaurant.
Having spent literally months trying to find the correct chilli sauce for authentic Pho recently, I'm sympathetic to that argument.
I suspect most people go out to have fun. What is fun? Meeting people and creating experiences/memories. Sure, you could sit with your friends at someone's home every night but that gets boring honestly and turns into the same people and patterns.
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.
Land is a serious problem except once it's no problem at all. If you don't know anyone who has land that they'll let you use, how do you find someone? Everyone I've met that plays paintball cheaply just plays illegally on land that they do not own, which may or may not seem unethical to other people. In my opinion, access to legal land actually is a significant hurdle for many people.
Now, in practice, paint is the main cost. Perfectly good paint costs less than $0.05/ball (maybe $0.03 is a bit low-end), which is usually marked up 100% or more if you're playing on a paid field (this is their main revenue). The problem is, many players are accustomed to a play-style where they burn thousands of rounds ($50+) a day. If everyone agrees to use pump-action guns (cheaper!), you can have nearly the same experience at 1/20 the paint cost. If everyone around you is using semi-auto and burning paint, it's a lot harder to go pump (some people like the asymmetric challenge, but most do not).