Like any big purchase I suggest you make a list of what you want to do on this new bike. ie. what type of surface do you see yourself riding on, how many miles do you plan to ride, how many days a week, What do you want to be able to carry as you ride.

Do some research BEFORE you go shopping, unfortunately not all sales people have bike fit knowledge. Handlebars can be changed, good components are a must, nothing worse than poor shifting or crappy brakes. A bike to big or to small is not going to put a smile on your face. Try out several bikes and I agree, perhaps you see one a bit above your price point so don't be afraid to search "lightly used"

Here is a really great series on bike fit to help you in choosing the right bike.

Enjoy,