The rails go for ~150 per side second hand. I heard auto technica make bolt on rails now and they are also ~150 brand new.
As for the seats, IMHO I wouldnt stick some copy seats in a GTR, i would rather go for a set of 33 or 34 GTR seats. I think just jap had a nice set of 33 GTR seats for $900, which isnt far off what your going to need to spend ie $400 for the seats and $300 for the rails. Also in terms of material quality even my friends genuine Bride's in really good condition have been UV affected, they have faded on the top section closest to the window. Also found his Bride Ergo's to be too firm(good for the track) but for everyday use i would much prefer my 33 GTR seats