Hi. I am female and 5'5'' ish. I wouldn't get too hung up on getting a female frame bike. I bought a 2008/9 Giant TCR C3 for £200 from Shpock a few weeks ago and I'm very happy with it. If the bike is a good fit, the crossbar isn't a big deal imo, unless you are going to your Prom on it. I looked for second hand women's bikes but found the choice quite limited.
If you are working and your company is part of the scheme, you can get good discounts on bikes via the Cycle to Work scheme. This might bring a new bike (and thus a wider choice) into your price range.
If you want to see some seriously inspiring women, including endurance cyclists, check out the lessonsinbadassery website, where a journalist interviews female athletes. My favourite is, 'I rowed the Atlantic on four days notice'.
Edit: Also, re frame size. Even if you are looking for second hand, it is useful to go to a big store like
Evans and try different brands as the 'size' is not necessarily the same in different brands, and whether it feels right for you is more important than being the 'correct' size. There's a big Evans near the Trafford Centre.