Used...try to find out your size, then hit craigslist/ebay. I don't think you'll find any new bike either mountain or road for that much. You might find a single speed for that price but thats not really somthing for a new person. You really need to think about increasing your budget if you really want new. The bad part about buying used is it will realisticly need to go to the shop to get checked out and maybe cable and cases, that will be about $60. This is not a cheap sport maybe you should borrow/rent for a couple days and use the bike like you really would and see how it goes.

New road bike budget is $800 or so and it goes WWWAAAAYYYY up from there..