I'm with Scott. You can use a bike trainer on your existing road bike (preferrable) or a mountain bike. Yes, it can stress your hub but there shouldn't be any damage assuming you mount the bike correctly and keep your weight centered most of the time so as not to torque it. I ride my steel frame road bike hard and my 180 lbs (on a bad day), don't cause any ill effects to the bike or trainer.
I use a Cyclops that I got on my local Craiglist for $100, used but great condition. Fortunately, the SF Bay Area is a hot bed for cyclists so the used market is pretty good. For a challenge, I use Spinverval DVD (http://www.spinervals.com/). Consider these just as hard as a real spin class. Try ebay, I'm sure you can find a bunch for cheap.
For the rear wheel, you'll want a cheap slick tire because any knobs will create a serious buzzing noise that will drive your housemates crazy. I bought a cheap, black road tire for $15. If you're paranoid about the back wheel, find a cheap rear wheel (which I did) and put your training tire on it. Then just change out the wheel when the bike is on the trainer. Assuming you have a quick release wheel, it's a 2 minute job. This whole setup will be WAY less than an elliptical and you'll keep your cycling legs all season. Now if you're real gung ho, you can get rollers.
http://www.youtube.com/watch?v=D4lA1Yd2JzcThere's a bit of skill involved and it's like riding on ice, but it's more natural than the trainer. BTW, I don't have the guts to try it...
