what's a original 7 1/4 duster rear end worth

The 7 1/4" axle is like the Slant six engines....Often times the only person that wants one is the dude that is just trying to replace a stock part that broke.
I've given away small bolt pattern 7 1/4" axles, small bolt pattern wheels, 9" drum brakes to guys that had incomplete cars just to get their cars complete again. It is situations like this that justify a hoarder mentality.