The 983S is a laminate-stocked rifle with iron sights.
Swap that stock for plastic, and drop the sights, and you lose at least $150 in the blink of an eye.
But you do bring up a good point.
The X83 models* are tube-fed, while the X82 models* use detachable magazines.
Depending upon the local market, one magazine type may be worth more than the other. (Here, the X83s sell for a little more on the used market. ...But some of that may also be that the X82s have often had the magazine(s) lost.)
*783/883/983, and "XT" equivalents; and 782/882/982 and "XT" equivalents.