Is it proline or a replica? It looks like a replica, as those are a tiny bit smaller. I looks legit and from a far looks to have all the Elway keys for his signature and the price (with the case) is definitely good. I have a Bronco D full size replica signed by Elway and I paid 300, which was a solid price for it.
Who is the COA from? And if there are 2, even better. One from the place that hosted the signing, and the second from a nuetral, third party with nothing to gain from claiming the piece to be authentic. Find out who the COA is from and do some research about the company or store.
Glad to have chimmed in before the usual, "Memorabillia is about how much you value the item at."