Having handled and fired the gun in question I can guarantee if it were placed in your hand you'd guess it's value in the $2000 range. (And by "your hand" I mean anyone familiar with 1911s)
Well that's kinda the point, if you add or subtract anything from the polymer it's not the same polymer. I'm not pretending to know what's going on behind MagPul's doors, just telling what I know from working with poly. We had additives for color, abrasion resistance, heat resistance, impact...