What is a fair price for a Miyata 20"?

I bought my son a Miyata 20" a couple of years ago it has a sticker on the
fork that says “flamingo” . He only tried to ride it a couple of times. The
tire still has the little rubber casting things sticking out all over. The
seat is like new except for a very small scuff in the front hard plastic
protector. He would like to know what a fair price would be to ask for it.
Thanks Please reply to ebourlet@gte.net