It has been my observation that it is a whole lot of things; demand, mostly. When I bought mine 9 yrs. ago, there hadn't been any for sale in this part of the country for a very long time. So, I got mine for $500.00
It had hardly been used, and was really in very good condition. It also had the Scrollwork, all of the attachments, a workable case, and a book. It sewed the first minute I tried it and gave and still does, give a beautiful stitch.
So, to me, it was worth it. I have seen our tech. guy, but mostly my own misunderstanding of how it works, and I had already worn out 1 bobbin case.
There are others who have paid as little as $200, but they had to have work done on them. So, guess it depends on many things what the price will be.
Mariah