We can all understand how you came to be bitten by the cycling bug! Since you have the Trek 7.2, why don't you start out by going to the store where you got that and try out some road bikes that are in your price range. That can give you an idea of sizing and handling. Go to some other bike shops if they are available and try some other brands. Once you get a better idea of what you like and what size you need, then you can start searching for a used one if you want to go that route. If you look around on this forum, you will find lots of advice on choosing a bike. Good luck!
Grits
2010 Trek 5.2 Madone WSD, SI Diva Gel Flow
2002 Terry Classic, Terry Liberator