Well I eventually want to get in to racing. For now though, just fitness riding and training I suppose. I doubt I'm going to be able to afford a race-ready bike in my price range though, so I'm really just looking for something to start me off on the right path. I'm considering selling my bike (it's an old 1997 diamondback 3.0 ascent, retailed $1000 back in the day) and getting a new bike with whatever I get from that.

Most of the bikes I see in thrift stores are the cheap walmart bikes, but I've been keeping an eye out just in case.
Yeah, I've been really tempted by some of the craigslist bikes that would just almost fit. I've seen a bike on there with a frame just barely too big with full dura-ace components for around $300. I was gonna buy it just for the parts alone, but it was too far away, and it sounded a bit too good to be true. Probably stolen.