My 1967 Laughlin Mantle PSA 8 is probably up there. Bought for $150, and the last PSA 6 sold for $275. There was a PSA 9 that sold by auction through PWCC for $103, but PWCC didn't put "Mickey Mantle" or even "Mantle" in the title, so it definitely slid under the radar.
So is it worth $400-500? Probably if I listed it as Buy-It-Now/Best Offer and waited for the right buyer. *Saw the Laughlin in the picture and thought it must be mine, but that's someone else's as mine was graded in my bulk submissions which popped a few days earlier.*
My Bazooka Panel of McCovey/Cash/Maloney got a PSA 9. The last 9 sold 10 years ago for $353. PSA SMR value is $600, but I don't think this set is as popular as it used to be. Will be putting it up for sale. Even with the SMR value of $600, it looks like they had no problem with it remaining on a bulk submission, but that also could be because the declared value of the entire order was so high that the order was still within tolerance for the overall insurance value.
The Stamps panel with Mantle/Bruton that got a 7 last sold for $265 in that grade, but even a 4 sold for $205. So again, another good BIN/BO if I wanted to sell it, but for now it's in my Master Set. Two 8s last sold for $1900 each. I will probably be reviewing this card a couple of times if needed, since it is pretty sharp. Here is a picture of it raw:
