Also consider a used mixte bike. I have recently purchased and restored several Peugeot Mixte's from the 1980's. Great bikes, fun, fast and lightweight. Awesome commuters, totally stable and fun to ride. And, not that expensive, even after adding upgraded parts as needed. Try Craigslist or ebay, although most people don't know the difference between a "women's frame" and a mixte frame, so you'll need to modify your search accordingly.