The price will vary a bit depending on the age and condition of the machine but if it is in good condition it is definitely worth somewhere around $1,500-2,000. Retail on the D160-R's was $6,790 so I think you should definitely be able to get a decent amount for the cutter unless it has any sort of issues that would need to be fixed.
Congrats on the upgrade to the new S2 and feel free to contact me if there's anything I might be able to do to help.
Best regards,
Phil Johnson
Airmark Corporation
(800)527-7778, ext. 112
philj@airmark.com