I sew pretty much everyday, for hours and hours at a time. I can wear out a relatively inexpensive machine ($200 - $300) within 2-3 years. As much hard use as they get, I just consider them to be disposable.
I bought a $400 machine this time, a Brother PC-420. Hopefully it'll last a little longer.
I do have a Singer 15-91 and a Featherweight, but to be honest, I never really use them. They're just collecting dust. I need fancier stitches and modern features often enough that I need a new-ish machine.