Hi Vegmama. If I were starting out with your budget, I'd probably go into a few bike shops to see what they have available. There are bikes in your price range, but you may get a better bike if you look for something used, or NOS. Some shops, like the one I go to (which is small and independently owned), have a great selection of used bikes in storage, which you'd never know unless you asked. My shop will also broker deals between buyers and sellers, which they've done for me.
You could also try Ebay and Craigslist. If you're in a place with an active bike club, there might be a bulletin board of stuff for sale with the club. There are often bikes for sale here on the forum, too. Usually, forum members will like to know you a little before selling to you, so stick around and go here:http://forums.teamestrogen.com/showthread.php?t=2001
The only other real necessities are a helmet and gloves, and your cell phone in case you need a ride home. You will eventually want shorts and jerseys, and shoes, but none of that is at all needed at first.
Once you find a bike you think you might want to buy, test ride it, tell us about it and the price, and someone will let you know if it sounds like a good deal. Good luck!