I bought mine off of eBay last summer, and had a fabulous transaction. Unfortunately, that seller doesn't have any up at the moment. (He's a retired attorney whose wife quilts; his hobby had been to acquire machines at estate sales and flea markets, peak and tweak 'em, and turn around on eBay.) I have about a thousand transactions, both buying and selling, and screened potential suppliers carefully; he didn't have a lot of feedback, but it was all positive, and my purchase would've been protected by PayPal. I also was patient, and investigated auctions and other websites for months. The end result was a gorgeous machine in its originally, nearly flawless case, lovingly cleaned and serviced, and packed with a bunch of notions... all for under $300 (including shipping.)
The deals are out there; just know what you want (I am anal, so a "pretty" and clean-looking machine was important to me), what you're willing to spend, and don't rush to buy too quickly.
Good luck!