I bought an entry level ($500) small men's bike this past April. Like you, I was new to the sport, and I didn't want to spend a lot of money since I wasn't sure it was something that I would continue with. I have been enjoying it, and it is something that I want to continue with, but it didn't take me long to realize that I had a bike that didn't fit me right. It couldn't even be made to fit me perfectly because it was a men's bike and the reach was too long even after changing the neck several times. Last Friday, I paid $2200 for an Orbea Onix Dama, and I am in love! It is so comfortable, and it's a dream to ride. I can't see ever needing any other bike. I'm so frustrated that I went and blew $500 on a bike that I replaced in 5 months! I hope that I can at least get $200 - $300 out of it selling it in the paper. If you've got the money, go ahead and get a bike that is going to last you...even if you have to use plastic to do it. I was lucky because my LBS was having a 2 years, no interest, no payments special if you financed through them.
Good luck!
Aimee
A bicycle does get you there and more.... And there is always the thin edge of danger to keep you alert and comfortably apprehensive. Dogs become dogs again and snap at your raincoat; potholes become personal. And getting there is all the fun. ~Bill Emerson, "On Bicycling," Saturday Evening Post, 29 July 1967