The biggest problem with buying a bike on eBay is the freight. That adds 10-20% to most riders, maybe more.

Look in the thrift shops. Look at the local bike shops (LBS in the parlance). You'll be happy with an 80's Schwinn lightweight, or a 70's-80's Raleigh. Probably your best bet at the thrift shops. Third, a real possibility is an earlier steel Trek. Any Trek, unless it is whipped completely, is a very good bike. There are about a million other bikes that would fit your needs - feel free to post any bikes you find here - there's a large group of expert knowledge here that can steer you in the right direction about any bike.