http://handle.dtic.mil/100.2/ADA953115

Above is a report from 1968 detailing the M16 rifle's procurement, cost, and performance history up to that point. Toward the end of the text is a mention of two proposed alternate manufacturers, Harrington and Richardson and General Motors, and their forecasted prices.

I can't imagine GM making that much money off of a small arms contract when compared to their automotive operations. Indeed, did GM even make any small arms after WW2?

As a point of interest (from the report):

" Colt's Inc. acquired the rights from Fairchild on or about 7 January 1959, at a cost of $75,000 plus 4.5% royalty on all weapons produced. Colt's contract with Mr. MacDonald (who recommended the acquisition) provided a payment of $250,000 plus a 1 per cent royalty on every rifle produced. (The fee to Mac Donald is referred to as a finder's fee and takes into account funds which he expended on exhibits and firing demonstrations throughout the world)."