What your father-in-law might be wanting to do is to "retro-build" an M1 carbine, ie restore an existing one back to what it was like coming out of the factory 1942-1945. You start with a restricted USGI (Inland, Winchester, Std Prod. etc) with mixed parts. In the collector's world called a "mixmaster". This is what you will most likely find for about $600-800. If you are lucky, the barrel will be correct for the serial number and receiver mfgr. But that's about as good as it gets. If there are more correct parts, you'll be lucky.
M1 carbines were rebuilt after WW II and parts from various manufacturer's were all mixed together, as they all fit. They are mostly marked/stamped with the mfg code. "Obsolete" parts were replaced such as flat bolts, push safeties, barrel band w/o bayo lug etc. These are generally not correct for '42-'44 build dates.
This is where it will be a challenge. Inland made the most carbines as a single mfr, so Inland parts are more plentiful, but not available from the USA as mentioned in other posts here.
For guidance, Craig Riesch's book is the best place to start, cheapest, but least accurate, followed by Larry Ruth's War Baby. Carbine Club newsletters (avail to members only) is the best place for accurate retro-mfr parts matching.
You could be looking at around $2000 in total costs by the time you are complete (which will take some time due to parts sourcing.
