Check this out for instance.
One thing you don't get with a used bike, however is a lot of choice to figure out the right size. To do this, you should go to a bike store and sit on several sized bikes of the model you're looking at. Then, you can shop the used market for that exact size. That's the downside of used - it takes time.
Size is important. While I'm an inch taller than my wife, she actually has a bike 2" larger size than mine. Her torso is much longer than mine. I rode her bike at the store and immediately it didn't feel as comfortable as the smaller one I bought.