If you can leave your ego at the door the most important thing is comfort. Unless of course you plan to race ect. Otherwise find a bike that fits you well with a decent groupo. There are differences between beginner vs. expensive bikes and like mentioned it's generally the groupo and wheels that make up a big part of the difference. Frames these days can also cost you 3,000 U.S. and more, which unless your made of money, or your frames are given to you, is a little excessive. When I made the jump from a steel Lemond to my Cervelo Soloist(not an expensive frame at 1200) the biggest difference I found was the power transfer wich each pedal stroke. Night and day. The cervelo seems to have no wasted effort with all power going right to the ground. It was also a better geometry for me as well, since Lemond's are very upright in comparison. Spend some time and ride a few bikes in your price range. I hear the Trek 1000 is a great bike for the money.
Best of luck