The responses so far have been "right on." The only thing I'd like to add is that you should do an honest assessment of what you need from a sewing machine before you choose one. You may find, as I did, that you can get a really good price on a machine that fits your needs but isn't selling well to others. I'd have never bought a Bernina had the 635 been a hit. While its sales were a huge disappointment to Bernina and its vendors, it met my needs, and I got a darned good deal. While I'm now Bernina-spoiled, I've never regretted my purchase.
On the other hand, NEVER purchase a sewing machine just 'cuz it's a "good deal." Know what you need and let that be your guide!