I bought a D60 Kurt like the photo above (no holes in the jaws though) for $120 about 2 years ago. If it was a newer D668 I would ask $400 if only used twice and was in as new condition. I've seen the D688 selling in the Seattle area for $350, new in the box, but I didn't want to drive 3 hrs to pick it up. There is a local supplier that has them new for $484 (toolssupply.com) which is where I ended up buying mine as I could pickup local vs shipping. All depends on what you have.
A good vise to look at for your mill is the Glacern 5". I had one of these for my Enco PF45 size bench top mill. They are very good quality and a nice size.