My issue with Thompson is the peice and if i was going to have one it would be one of the more desirable ones... to much money for something with no modularity.
As a functional weapon, MG-42 converted to 7.62 nato or just a straight up MG3. Or a full auto AR lower to be built up as my go to shtf rifle. If its a collection thing, I'll take an StG44 or any of its developmental (and largely identical) variants. Wouldn't mind a Suomi or MP-40/38 either.
this+ suggest you aim higher... M31A with 9mm conversion kit (cheap to shoot and and worth a fortune) as only one OEM conversion has been found to date