After WWII the US M1 Carbine was copied and produced by a number of manufacturer's including Plainfield (Iver Johnson), National Ordnance, and Universal. Most copied the GI design, and used surplus government parts except the Universal. It is not compatible with government parts and used cost-cutting features such as a stamped-and-welded operating rod and cast pot metal trigger guard assembly.
If it is an M1 Carbine copy, $150 is a reasonable price. If it is a real GI M1 Carbine in good condition, it is a bargain. Inspection of the manufacturer's stampings behind the rear sight will show either one of the ten WWII GI manufacturer's markings (Saginaw, IBM, Rock Ola, Winchester, Irwin-Petersen, etc) or the post WWII commercial makers.
HTH
John