I'm not an expert by anymeans, but have just recently gone through the same process you are. I was looking to buy 2 bikes... One for me and one for my wife. And like you, I was willing to spend about $300 each. As I shopped around, I realized that any new bike that was $300 or less, tended to be kind of crappy. I'm one of those people that does not like to be limited because of the equipment I'm using. I decided that there were no new bikes in my price range, that I was willing to ride. So I started looking at used bikes. I hit Craigslist, ebay, classified ads, and started asking friends. I was able to find 2 bikes (that needed minor work). I bought a Giant for myself for $50. Then, I bought a GT for my wife for $75. After taking them to the local bike shop, I was able to recondition the 2 bikes for about $200. So, for around $325, I got 2 really good quality bikes. Both have better than average components, are lightweight, and (after a little service) are in great condition. I could not have bought these bikes new for the price that I paid.
Just my experience... hope that helps.