You can find a decent used road bike for under $300, or a new one for about $500. You could also get a hybrid for just a little bit under these prices, but you might find you enjoy a road bike more. It all depends on how you find yourself riding.

In my opinion if you're riding on the road you ought to get a road bike. The only positive aspects of hybrids, in my opinion, is that they're cheap. I was going to get one until I happened upon an old road bike at a thrift store for $15. I'm so glad I'm into road cycling now, it's sort of like having a sports car when other cyclists have SUV's (mountain bikes that never go offroad!).