I bought what I thought was an Underwood M1 Carbine about 3 years ago, only to discover it was a Quality Hardware carbine with an Underwood barrel. I was trying to build a "WW II Typewriter Arsenal - Underwood, IBM carbines, Smith-Corona M1903A3, and maybe, someday, a Singer 1911.
Remember, during WW II these guns were assembled at the factories with parts available - so it would be common for a carbine (and Garand, for that matter) to have parts from several different suppliers. In the field, armorers would fix them with whatever parts were at hand.
After the war, most of these guns went back to the U.S. for arsenal refurbishing. Again, old and worn parts were discarded and new parts put in their place. So getting an "all Underwood", "all Inland", or "all Winchester" would be next to impossible.
And remember, most of these went through the Korean War as well, so the same thing occurred in the 1950s.
Last I heard, CMP was out of M1 Carbines. But yes, market prices are around $800 - $1000 for USGI carbines.