Congrats on your progress, 45 pounds is quite an accomplishment. I lost 15 pounds by just biking ever day to work.
My bike suggestion would be a KHS Green. It's a little different than the bikes you've considered - it's more of a true hybrid. It's geared toward people who want to use their bikes to get placed and get things done (rack, 3 speed). It should be availabe in your price range. I have it and quite happy with it. Think about if you need all those gears, I started out with my old mountain bike, wasn't too much to get it fixed. My local bike shop was quite helpful in that regard.
Keep us posted what you decide on doing...