8gb cards, either rx480 or 580 are in demand by miners and so it will sell for pretty penny. I'm not sure how much but I'm guessing you can get around 14-15k for it, maybe moreon behalf of a friend - price check on an rx480 8gb? no warranty and one week testing period
There are lots of people who will PM you, most of then are lowballing reseller scum. Do not indulge them. If you want to sell, please follow the rules by creating a thread with pictures.