[Noah930]

I have a GT Avalanche (mebbe from 1996 or so?). Don't know how the current ones compare, though. But it would definitely be overkill for what you want out of a bike. I think I paid about $900 for it.

If you're only going to be on roads, and doing this mainly to lose some weight, then there's no need for an aluminum/titanium frame, higher-end off-road worthy components, or rear suspension. It's nice stuff to have, and you'll notice a difference in the weight of the bike, smoothness of shifting, etc. But you probably won't notice a significant difference in what you're trying to accomplish (fat-burning, cardio, basic exercise). If anything, you'll notice that you have to ride longer/faster/further/harder to get the same workout. You will notice a difference in the cost of your rig, though.