Garmin Montana 600 question

Guys I need a little input here.
I have, or rather my wife has, a Montana she just bought and she does not like it So! It has to go.
My question is what is one of these worth used with North America maps and the motorcycle mount , I don't want to get ripped but on the other hand I want to be fair.
Thanks for the help.
Ken

Most folks won't pay more then 1/2 to 2/3 of the price of new. Good luck with the sale.