You're seeing the publisher's list price on various sites. That's because if the publisher can provide the print, they will give a dealer a 50% discount which is around the market value from the secondary market. It's very unlikely you could sell your piece for more than 50% off that price or $2500.00. You can place a classified ad on several sites including a visual (which they usually can provide). I'd recommend
www.artvestgallery.com because I know the owners.
An appraisal by an accredited entity will cost around $350.00 and more than likely they would appraise the piece at between $750.00 to $1500.00 as it is a commercial manufactured print (the artist did not make the plates or pull the prints but just signed and numbered). The original publisher's markup is so high that appreciation is not possible, at least not for 50 years or more (if there is still a demand for the artists' work which is remote -- he's not of museum quality).