It is a lot of dough.
But it is rare (and it is signed - all of the Post Office HC firsts were), and you won't find a cheaper copy in the same condition.
I don't know that I've ever seen any copy in this condition. And if "condition is king," as most collectors will tell you, the price isn't too high. If it was on ABE (or when it gets to ABE), it will likely be listed for twice what he's trying to get here.