So...what kind of bike do I need? (college student)

[Cataboo]

If you're 5'7 for a road bike you're probably in the 50-54 cm range. In a mountain bike, you're probably in the 16" range.

If you're commuting on it mostly on road - you really don't need a suspension on it, at the most you want a front suspension.

If you want to ride on trails for fun, I'd say stay away from skinny road bike tires, you could swap thicker tires & tubes on to make it more comfortable - but given your price range, you really should buy about what you need and then upgrade the seat for comfort.

[newfsmith]

Try recycled cycles in Seattle,
http://www.recycledcycles.com
Also try contacting bike clubs in your area, they may be able to direct you to appropriate sources. Don't be afraid to go to any bike shop. Be clear about your budget. If they can't help you, they are likely to know where you can go. Scan the volunteer pages, many "earn-a-bike" programs give credit to volunteers that can be applied to purchases and some have adult EAB's. Google for earn-a-bike to find a location near you. Try browsing the bicycle paper for shop and club locations. http://www.bicyclepaper.com