The Cadmus is a firm stock as it folds and locks, the ones that pull out (like this ARMSLIST - For Sale: M1 Carbine adjustable stock)
 are not stable, I got one on a trade with a carbine and could not get rid of it fast enough. M1A1icon repros are ok but they don't truly lock open and can start to fold while shouldered with a little pressure the wrong way. It only sells for big bucks if it sells, they can ask anything they want.