How much do you think one would get if they sold their premium leather heated and cooled seats. I kind of regret not getting recaros and I might get a pair of leather ones from Ford racing?
I'd imagine if you are selling front and rear - being this is the first year for those seats and the design, you could easily get $1200... If only fronts, probably a quick $800 for the pair.
Over time you will get less as more become available to the public.
Another note:
The 2015 Mustang plain black leather won't command much, but the optional colors and those with the optional stiching will most likely command more $$$.
For instance, the 2003/04 Mustang Cobra seats were selling for $1k just for the fronts only when those cars came out (because of embroidered Snake logo and different color center section) - now you can pick up a complete set of front and rears for $500...