I haven't looked into what the market price is and won't bother until I find the Dolby C unit. I'm sure the unit will need to be serviced with new belts and other rubber parts (idler pulley, etc.). As I remember, there was a slight problem with the azimuth alignment that needed correction as well. I'd probably hope to get two or three hundred below market for it, selling it "as is".
It's a phenomenal tape deck and more than you could expect. The fact that it will optimize the tape head angle automatically for playback and recording is amazing. It weighs about 50 pounds, so it's a bear to lug around. When you take the cover off, you're astounded with the bulk of the innards. It takes up nearly every bit of interior volume within the cabinet. The picture doesn't do justice with that glossy case - it's a great tape deck and a work of art at the same time! It definitely grabs the spotlight in any setup for its imposing looks. I don't know if you can see it or not, but even the buttons (play, pause, etc.) illuminate on their perimeters, so the play button looks like a glowing triangle.
I went through several cassette decks in the late 1970s - JVC, Pioneer, etc. before buying my first Nak - a used 550 (portable). I never considered anything else after that, having a 680ZX and buying other cheaper decks (BX-125, etc.) for family members. I might have had a ZX-7 too...can't remember. This one I got for about $2K as I remember. I forgot what the Dolby C unit ran, but I still have purchase records stashed away - 1984 I think. For a cassette deck, I don't think there has been any better - with the "signature" edition being the exception for its beauty - but you sure pay the price for that (unless you're Oscar Peterson, of course).