It's interesting that you mention this, as Shotgun News just featured an article on the M2 Carbine. According to Pete Kokalis, the M1 Carbine entered production in 1941, but was only made by Inland initially. Additonal manufacturers started in March of 1942 through early 1943, in order:
Winchester
Underwood
National Postal Meter
Rock-Ola
Quality Hardware Machine
Pederson
Saginaw Steering Gear
Standard Products
IBM
I don't think that Iver Johnson started making these until the 1960s, I recall seeing them in the Sears catalog in the 1970's. So, if you have an Iver Johnson, then it probably isn't made in 1941, and if it was made in 1941, then it seems likey to be an Inland. WWII guns seem to be fetching about $600, +/- $150 depending on many things. Johnsons are going to be a lot less.
H
(And I found a link to a history of these things at
http://www.fulton-armory.com/M1Carbine.htm)