First, $37.99 is a good price for any proof silver eagle in original packaging. Second, the 1987-S proof is fairly rare in PF70 (perfect) grade. PCGS has only certified 101 as PR70, out of 6053 certified. NGC grade 70 coins usually sell for less than PCGS ones and the PCGS price guide lists $4000 for the 1987-S PR70 (full retail price in a PCGS slab), but even $1150 may be a little high. The chance of a uncertified coin coming in at PR70 is slim to none for 1987 coins, if anyone who has handled it over teh years thought it might be perfect, it would have been slabbed. PCGS lists the 1987-S in PR69 at $65 and $42 in any grade below that. Most likely the uncertified coin is a PR69 but it could be PR67 or PR68 also.