

Help determining the value of a unique alter
Unfortunately after playing collecting MTG for almost two decades I have begun selling off my collection to help cover the cost of my new child. (Actually an exciting thing!!!) But with that being said I have a pretty unique card in my collection that I haven't been able to trade in to local game stores as it is an alter. The trouble is I think it is worth quite a bit of money and I need some help with evaluating its worth and getting it to the right person.
It is a 1999 World Championships Tokyo Gaea's Cradle with, in my opinion, a gorgeous full card alter on the front.
Would you guys be able to help me or point me in the right direction?
Picture for context.