Figure out the size frame you need first, more important that it fits right rather than price.
Most of the undergraduates in Ann Arbor ride
mountain bikes, anything from a Wallyworld Huffy to a tricked out Specialized. If you're on a budget and want a sturdy bike for less than $150 in ready to ride conditon, I'd be looking for a chromoly steel framed mountain bike, rigid non-suspension from the mid 1990s; Trek 830, 850, 930, a Gary Fisher Mamba, Aquila, or Wahoo, a Specialized Hardrock, Rockhopper, or Stumpjumper, or a Schwinn Paramount PDG, High Sierra, Cimmaron, or High Plains. You can look for a GT, Miyata or Univega as well, but probably harder to come by. It's easy enough for $30 to install 26 X 1.5" wide road tires and tubes in place of the knobbies and have a mountain bike ride as nice as a hybrid. Last month, I paid as little as $25 for a HardRock and $62.50 for a Stumpjumper; only the HR needs work.
Most of the college and Rochester/Syracuse probably have bike coops that sell reconditioned bikes and can help you learn to ride as well.
TREK 850 @ $60
http://rochester.craigslist.org/bik/4234453562.html
Giant Nutra Hybrid #@ $90
http://syracuse.craigslist.org/bik/4264895928.html
Trek 930 @ $75
http://ithaca.craigslist.org/bik/4262638257.html
Ideally, the wheel rims should match in color and profile, the rear derailleur would be a Shimano Alivio, STX, or Deore. And don't wait to get approval here if it looks like it's priced low. Just jump on it.