I used to be into the high power rocketry scene (was an early member of Tripoli Rocketry Association) while I was in college. I bailed out when I decided things were getting too expensive. At the time, there were no hybrid motors and reloadable motors were just beginning to be introduced so we were pretty must stuck with single-use motors. Like most hobbies, there's the desire/pressure to build something bigger, faster, higher altitude, launching bigger payloads (launching VHS camcorders using an 'L'-sized motor wasn't unheard of). When my addiction got to the point where I was spending, say, $50 or $80 per launch, I decided I just couldn't justify it anymore. It's an ideal club hobby though where you can divy up the costs. When hybrid motors were introduced, it almost lured me back into the hobby but by then I already had more than enough hobbies to absorb all my discretionary cash.
I still have most of my old rockets though. They tempt me every time I open that closet door.
Edit: I think the final straw, though, that caused me to leave the hobby was my disgust after losing a fiberglass rocket due to a failed parachue. I spent a good 4-5 months constructing that guy. *sniff*