A good price is dependent on how much use the machine has had. If used daily for a quilting business, it would be worth less. The options on the table (hydraulic lift, electric quilt advance) add to the price. Also, what add-ons are included, for instance Hartley Fence, Extended Base, Circle Lord, Micro Handles, etc. Are shipping and setup included? This could add an additional $500-$900 to the price.
And finally, what would you consider an acceptable price to purchase the machine?
I've seen 2000 - 2007 model Milleniums sell for $9,000 - $15,000 on the APQS site. A 2006 model recently sold for $11,000.