It's rare.. so there isn't an agreed value, it's more what you think it's worth.
If you collect rare pins and need this last one to complete your sonic collection, you may value it much more..
if you're a player and just want something new or fun to play, you may value it less.

Personally I wouldn't trade a demo man for this.
Hang On looks like it could be a system 11 game, I wouldn't trade it for a wpc game.
Also the Sonic has all special boards, if something fails you may have a big problem to have it repaired / replaced..
if something fails on your demoman you can fix it as all parts are available..