Price depends on many factors. Check the Gun List, and online: gunsamerica.com, gunbroker.com, and Auctionarms.com.
Also check the Blue Book of Gun Values, and The Standard Catalog. These should give you a good idea.
GM carbines were made at Inland, and Saginaw divisions.
Which division made it will be stamped under the rear sight.
General Motors Inland, made the majority of carbines, and almost certainly the best quality.