The Guild Economy M-20 was a small bodied acoustic flat top, available between 1958 and 1972 - effectively the same specifications as the Guild F-20, but with a mahogany top rather than spruce.
The Guild Economy M-20 was described as follows in the 1963 Guild catalog
A fine quality concert size guitar at an attractive budget price, made possible only by the most modern production facilities in Guild's enlarged plant. This lowest-price Guild offers most unusual value. Has the fine construction and features for which Guild is famous, including Guild's fast-action mahogany neck with adjustable steel neck rod, finest rosewood fingerboard and pearl position markers. Honduras mahogany body is 13 3/4" wide by 18" long by 4 1/8" deep. Tortoise color pick guard, rosewood bridge, nickel-silver frets. Equipped with non-slip tuning pegs and Guild Strings.