From what I understand, you're in a healthy biking community, i.e. there should be a lot of used bikes around. Try craigslist.org. As to a new bike being better, making sure it fits and does what you want is most important, and new bikes that don't do that are just expensive crap (for you, at least). So, if you are totally unsure, getting a used bike to find out might be best.

Think about where you will ride it, what you want to do with it, how far you want to go on it. If you want to ride streets sort of fast, think about a road or cyclocross bike; if you want to do some trails and short stuff in town, think about a mountain bike. If you get something used, take it to an LBS that will help make sure it fits, not just when you are standing over it, but also seat height, handlebar to seat distance, handlebar height. Then, try it out and find out what you want to do. You have a whole lifetime of biking to find out what kind of biking you want to do, and you'll need to learn that from experience.