This is my grail gun, too. Some guns hum a little "buy-me, love-me, take-me-home" tune when you fondle them. The 1928 Thompson sings to me like a siren calling a sailor onto the rocks. All that stops me is the fact that owning is completely out of reach. I am lashed to the mast and cannot break free. If someone left me 50 million, I would start the paperwork that week, before I bought a new truck, talked to a financial adviser, or even picked out the safe I was going to put it in.
I have shot a Thompson, both the 1928 and the WWII configuration, several times. Won a club full-auto shoot and the over all high shot for the day using a 1928 Thompson, a 1911, and an AR-15 on one of those occasions. There was a member of my club that had a large collection that included several full-auto weapons. He had purchased them decades ago when new ones could be made, and while they were relatively expensive, they were were still within reach. He was generous with his toys and would set up range days that gave us access. He has passed on and it seems unlikely that opportunity will come my way again.
Here's one for $19,995. It sings to me. The Wiki article is a good jumping off point to read about the Thompson. There's information about the variants, the modifications during the production years, weights, rates of fire, and more. This time, for me, it's not academic. Here's a gun pr0n image and a video. Click on the image to biggify.
retired FBI agent, John Wallace, that appears at 40:14 is the man I knew and that Thompson is one that I got to shoot.