Visit every bike shop with ten or twenty miles of where you live, and tell them what you are looking for. In my area, I sometimes run across bikes for $200 or $250 that a bike shop took in as a trade. It might be a 1987 model, but after the shop tunes it up and trues the wheels, it will provide a ride that is just as nice as most new bikes in the $500 to $800 price range.
The bike shop in my neighborhood recently had a twenty year old road bike that looked brand new. Someone bought, hung it in the garage and never rode it. The shop was going to sell it for around $200, which was about what just the wheels alone were worth.