I'm sure others will chime in, but if you can find a nice used one with at least tiagra 9 speed parts or better it should be fine (I'd skip any bike with sora or lower components or anything without integrated shifters). You should be able to get a decent used one for around $500 and sell it to close for that later if you get something else. I have found it's a pain finding a decent used road bike in that price range though, it's a lot easier getting good deals on used stuff that's more expensive but a great deal.
If you don't want to deal with the hassle, you should be able to get a decent new bike for around a grand or a little over or you might be able to find a low level bike at performance or whatever that's an ok deal.
If you find you love it, then go out and get an awesome new bike and hopefully by that point you'll know what style of riding you like, what gearing you want, etc and can buy exactly the bike you want. I spent $2500 on my current bike, but the hours I put on it a week (usually around 10 which isn't that much compared to a lot of people), I figure it isn't really that expensive for how much it's used.
I did a quick search and the only thing half decent I saw was this
http://sfbay.craigslist.org/nby/bik/3974785424.html