If all you know is that you want to buy a bike that will get you around town and won’t cost an arm and a leg, these are what you should be looking for. Just make sure you get the right size and that it's in good shape.
If you want a road bike, look for one of these. They are fairly common, and the steel frames on these bikes were often made in Japan with a high level of craftsmanship and materials.
I use the term “semi-classic” to describe these bikes because we aren’t looking for something made in the 70’s, but rather the mid-80’s or 90’s. Why this era? Because bikes from this time period are new enough to have components that work well, are light, and are easily replaceable.
What specifically to look for:
Depending on the condition of the bike and your market, expect to pay anywhere from $150-$350.
Older mountain bikes are basically budget hybrids. This bike should work well for the general commuter, and the frames often have spots for racks and fenders to be added on. By fitting some road-friendly “slick” tires on them, you'll barely have to worry about potholes and crap pavement.
The better ones will be made in the early- to mid-90’s, for the same reason as the road bike above: new enough to work well and have replaceable parts. Also, because older mountain bikes aren’t in great demand, they tend to cost less.
What specifically to look for:
Depending on the condition of the bike and your market, expect to pay anywhere from $100-$300.