I have two berninas as well. One is about 30 years old, an 830. It's a never fail machine and the stitch quality is awesome. I also have a newer model, about 10 years old, and it, too is wonderful. It has a different selection of stitches and I use them quite a bit.
I have seen 830s on ebay for around $400. Cleaning my old bernina is one thing I really like about it. Almost all the moving parts are accessible and can be oiled. That's pretty important, as where I live they charge somewhere around $100 for a machine cleaning and keep your machine for as long as 2 weeks!!! Consequently, they don't go in as often as they should. I can't afford that!!
Good luck!
M