They don't show up often, but I acquired this, along with several other pieces, in an auction a few months back and had it authenticated and encapsulated by PSA. Hard to price, but based on other sales and its scarcity, as well as the length of the letter, I'm looking for $6,000 and listening to offers.
Lots of vouches.
https://photos.app.goo.gl/u4qJw8GeyGXw4P2G8
https://photos.app.goo.gl/E2T5py4Z4VLkqgZL9
https://photos.app.goo.gl/97VMt6AbFD7mvfQx6