My special interests are creatures and making art.
I enjoy creatures by learning about animals online/in books, looking at monster art, observing bugs and birds outside, etc. so that doesn't cost me anything.
Making art can be dirt cheap or extremely expensive, depending on the medium and materials needed. In my case, it only costs a moderate amount. I use expensive materials sparingly, and my larger projects are typically made with things like second-hand fabric and pieces of plywood.
I think another factor that balances things out is that I don't have a lot of interests outside of those two things that would normally cost people money. I don't travel, I rarely drink, I don't go out to restaurants or to social events. Outside of living expenses like groceries and bills, I only really spend money on art related things.