value of AR-15 upper with 1:12 twist barrel?

[hans g./UpS]

Any guesses asto the value of an excellent condition AR-15 upper[with shell deflector,bolt assist, front sight and bolt] that has a 20"cryogenicallly treated 1:12 twist barrel?
I'm considering one of those STAG L  left hand uppers  instead.
Thanks.

[rangerruck]

lets put it this way, the heaviest bullet you can use with this and still hit the side of a barn is about a 60 grn bullet.  i have a superaccurate cz with that twist, and once i get to 62 grn , i have no idea where the bullet might hit.