A couple more prices for you:
5” M&P with Speed Hammer, post-war Diamond Magna (not specified as serialed to the gun) reblued, nice condition, sold on GunBroker 8/7/2022 for $1245. S/N C54767
5” M&P with Speed Hammer, post-war Diamond Magna (non-numbers matching) sold on 6/23/2022 for $2500. Ship date August 1950, S/N C69070
4” M&P with Speed Hammer, white plastic aftermarket Magna grips sold 8/8/2022 by Salt Lake Collectibles for $1125. I think this is the same gun RWJ referred to.
It appears that there were at least 2 production runs PostWar, some with the PreWar long action and others with the PostWar and Speed Hammer. Due to the overall scarcity of the .32 M&P I’m not sure if there would be a price differential between the two versions.
The only PreWar M&P in .32 Long in my database is one I purchased via GunBroker auction on 1/23/2022 from The Range by Jimmy Primos. It was advertised as a Regulation Police but it seemed obvious to me that it was a K-Frame so I took a chance and bought it for $1390. This was a special gun built on a M&P frame with PreWar K-32 barrel and patridge front sight. Stocks were not numbered to the gun. It was in excellent condition with some slight freckling. Note that the S/N 677992 is in the range of the PreWar K-32’s. So far as I can determine this is the only .32 Long M&P with a 6” barrel.
The factory letter calls it “the .38 M&P Special Order Variation .32 S&W Long. Its production was authorized by Douglas Wesson, S&W Vice President.
I purchased this as a shooter, but realized that it really belonged in the hands of a collector so sold it at auction via Jim Brewster, S&WCA Secretary, Sarah15 Guns, and it brought $4500. The gun went to a well known collector.
Here is a link to a discussion of the PreWar M&P:
.32 Long M&P Arrived Today - Letter Update