My primary commuter bicycle is a 1986 Univega Arrow Sport. Bought off craigslist for $160 and worth every penny. It needed nothing.

Here is a general article worth reading if you are serious about buying used.

Buying used maybe confusing but there are many people that have traveled this path and can offer you loads of advice. Even doing a search for "used bikes" (titles only) will unveil alot of good information. That said, I know used bike shopping is not for everyone. It does require some degree of mechanical knowledge and motivation to do some reading. It will require patience to find an acceptable bike of the right size and right condition on craigslist. If you are willing, this would be the best way to get the best bicycle possible for your hard earned money in my opinion.