I think there are many factors that would effect the market price of an easement between willing seller/buyer. But if we get to a point of legislative action/eminent domain...I doubt the compensation will be anywhere close to 5 figures...as explained by VG.
It won't happen over night, but with digital/online mapping availability, a growing interest in the outdoors, and the increasing political target on the 1%...its only a matter of time before those who attempt to block public lands by corner crossing arguments find themselves out in the cold.
Its very telling that there are really no corner crossing tickets...shows who has the most to lose given so many people cross corners every year in western states.