On my list of firearms to aquire is a Thompson.
Don't ask me why, I don't really know.  
But the real question is--
Do you ever see Thompson drums for sale?

500-1000 $

Keep checking "subguns."

They are really pricey. Typically, the L drum (50 rds) will sell for $600 and up. The 100 rd drums are out of sight ($1000). So you can pay more for the drum than you paid for the gun.

Just load up on 30 rd stick mags unless you have money to burn. Or you can get the "look" with a 10 rd drum. It is just silly to spend all that money on a drum magazine that you won't use much if at all.

Of course I have one that came with a "preban" Thompson in a violin case.