It’s perfectly possible to enjoy hobbies deeply without getting “serious” in the way you describe.
I’ve taken my 10 euro dance classes for years without feeling the necessity of pricey exchanges and camps.
My neighbour goes to the park many evenings to play petanque, doesn’t cost him anything.
A couple I’m friends with goes on day hikes where they do bird watching—maybe they bought a nice pair of binoculars once? Another couple likes to lay jigsaw puzzles together, not exactly breaking the bank!
My sister is learning Finnish because she never learned a non indo-european language. She bought a book.
I would wager most people’s hobbies are low key like this because either they don’t have disposable income to spend on them, or they don’t want too!