first, congrats on the weight loss and putting that many miles on your current bike. changing to a road bike will be a large difference in feel. you should test ride a few before you commit to changing styles completely. i would recommend test riding at a local bike shop to find out what size fits you. they may even have something used in your price range. size is very important. it will determine, in large part, how comfortable you are riding.

once again congrats to you and keep up the good work. i love seeing fellow bike commuters on the road.