^This
I've been researching M1 carbines as of late since it will be my next purchase on my aquisition list and from what I gather the early companys, that produced the USGI weapons such as Inland, IBM, Saganaw, Rockolla, & such have the most value. But, and as with all battle used weapons there is a but, the value fluctuates dependant on original parts vs refurbishment.
To find an original M1 Carbine with it's original all matching parts is rare and drives up the "collector/safe queen value". The vast majority of these though, due to post war military potocol of storage of the weapons, was to disasemble them and seperate parts into buckets such as Trigger groups in one bucket, barrels in another, recievers in another. So when they were bought up and reasembled durring surplus buys most of them were a popperie of manufacturers due to the interchangability of the USGI parts that had strict parameters the different manufactureres were given when they initialy forged the parts. That is also a reason the "commercial brands" such as Universal or Plainfield hold low premiums because without gunsmithing the USGI parts don't fit the rifle properly and may cause safty issues.
So, price is dependant on stripping it down to see exactly what you have. Lightining in a bottle? Or just a really nice USGI gun that has a bit more value than a commercial equivalent.
Thats all I got though so far in my research so I don't have much more to offer on advice.
EinfieldGuy is right with the valuation, alot of variables affecting the price.
Good luck with your research.