I have a Banjo Mandolin thing How Much Is It Worth?

I got a banjo mandolin thing from my granddad ages ago, he thought it was a banjo but it wasn't. I did some googling to find out what it was. It has 8 strings in the formation like : !! !! !! !! and the backing is a little damaged. Its quite small but not as small as a ukulele. Its been re stringed. If anyone could tell me if its worth anything or its a piece of junk would be great.