How much cash can I get for my 71 Maverick?

My granpa had a 71 Maverick in his barn. Well he's gone now so now it's mine. It has 30k Original miles stright 6 cly. For being 40 years old it has little rust, I mean it has rust but mot much. I put some gas in it & started right up. What do you think it's worth & where do I sell it? Thanks