That is a good price. Especially for a '42. That can be confirmed by S/N at oldguns.net.
If anybody tries to tell you it has matching numbers he/she/it doesn't know what they're talking about. The numbers on M1 Rifle parts are drawing numbers and have nothing whatever to so with the S/N. Said drawing numbers on the barrel will tell you the year of manufacture. Doesn't matter if the receiver and barrel are made by different companies. Not a bad thing if they were though. Ditto for the other parts, but matching part makers on M1's was mostly likely made that way by somebody with too much time and money. Weapons techs did not and do not care who made any part they replaced.
Start with the general condition, then the barrel, then the gas tube and op rod end(there are dimension specs you can check if you can and have a vernier or micrometer). If you have one, putting a loaded cartridge, preferably an M2 round, in the muzzle will let you see how far the muzzle has eroded. If the muzzle swallows a bullet, it's worn. Possibly to the point of worn out. Not a safety thing. Just an accuracy thing.
Try and look under the stock for rust too. Just a field strip will do. Excess pitting is a bad thing.
Millions of rounds of factory ammo have been fired out of M1 Rifles long before there was such a thing as an adjustable gas plug.
Try and get the seller to throw in some clips too. You can't shoot the thing, semi-automatically, without 'em.