I sold my 650 used a few years ago. My package ran about 1k new. I sold it used for 850-900. Bobcat probably has new, and used in stock so you can compare pricing.
I have to agree with M67, I wouldn't sell mine for even the price of new, just because that would mean I would have to get a new one set up and dialed in. Buy a new one and enjoy the smell of BLUE KEWL-AID when you open the box.
There was a 550 in the classy section yesterday with a bunch of components and stuff. It went as soon as it was posted and for about two hundred off new.
There are deals be aggressive and have the cash ready. Buying used is good because you will most likely get all the extra goodies that will not come with a new one.