Originally Posted by no1mad

A lot of variables to consider, though.

Going the CL route, the OP might luck into one in decent shape at a fair price. If something needs work, however, the costs can escalate rather quickly for a novice that doesn't have a well stocked parts bin or has to rely on the LBS for repairs. IF the OP still intends that the bike will be a short term thing, a rental takes away the hassle of assessing the condition of a potential acquisition, servicing it, and then reselling it (most likely at a loss).

However, the OP is in SF, where he has access to co-ops and bike kitchens- I suggest the OP explore those options first when buying used.