I've got something similar, but it's a calendar from the year 2000 signed by the entire squad along with Sir Alex Ferguson. A family friend used to work at United's training ground and my parents secretly asked them to do it for me as a Christmas gift.
Why on earth would you even think about selling it though? Mine has been locked away in my parents attic for years, along with all my other football stuff so it doesn't get damaged or lost. Even if I was destitute I would never consider getting rid of it.
I've got a match-used Mitre Fluo Flare ball from the late 90s which would probably sell for a tidy sum too, but again it's not something I would ever want to sell.