There are several variations of New York addressed Thompson drums with differing rarity, hence value. As for the WW2 Bridgeport drums as well as the pre-WWII drums, the pricing varies considerably based on correctness (swapped rotors and wrong winding keys being a couple of potential issues), and condition (dents, scrapes, rust, and the like). The best website for Thompson SMG information on all topics is the Thompson Submachinegun Forum Message Board at Machinegunboards.com There's a pinned topic illustrating all variations of Thompson drums.
Good luck.
MHO, YMMV, etc.
