Besides children, most of my other hobbies didn't really begin until after college--when I got my first job and excess cash!
As a kid, I enjoyed reading and playing video games. I still enjoy both, but nowadays I borrow books from the library and go after retro games (pre-PS2/GCN/Xbox).
After college, my hobbies in chronological order were:
fountain pens,
playing cards,
tabletop games,
toys (mostly Japanese action figures), and finally
mechanical keyboards.
The three I still continuously enjoy are reading, video games, and keyboard paraphernalia. I still like fountain pens, but do not use them enough to justify frequent purchases. I love me my European-style board games as well, but my friends with whom I used to play have all moved away so I don't play them much anymore.
Addendum:
I guess I also enjoy lifting weights more, especially as of this year. In high school I was active in sports throughout all three seasons, and since then have kept exercise in my life in some mode or another.
Post addendum:
Whoops; exercise isn't really "expensive" for me as I get a membership at my office building's gym.