Test ride a lot of bikes. Try out different geometry (WSD, "relaxed" competitive road, aggressive (more crit racing style) road, etc.) and different brands (which will also have different geometry). Ride in your price range and see how the "ride" is, but if you intend to race in the relatively near future, you will probably want 1) a light frame, and 2) good components. That may take you up in budget a bit, but then you will be less inclined to want to buy a completely new bike in a year when you're into racing. You can get a cheap light frame, like a Cannondale aluminum frame. Or you can go with carbon if you prefer the ride, but it will cost more for a decent (light and stiff) level of carbon. The components will probably be what will annoy you the most if they are a bit too cheap, because they could take more maintenance and might get obnoxious to deal with in terms of performance if you're going to be doing group rides with racers and starting to race. That doesn't mean you need a $2500 Dura Ace 2900 groupset. Something like 105 will be plenty good for a beginner racer. It's just that you may not find that on a sub $1k bike unless it's on a good sale. Things like wheels might be not so aerodynamic and heavy, but those are an easy upgrade later if you save up for more race oriented wheels. Something nice and durable is a good way to start there.

Also, if you're going back to school, see if your school has a team. It's a cheap way to get into racing and there are some good intro categories. It's not a NCAA sport, so there are no eligibility rules as far as age or years in school. You're just supposed to be a full time student.