Right now they seem to be going for $10-$14K depending on condition and options. Roush didn't start tracking VINs until 2001. Prior to that some where built on site at Roush in MI, some where done at Roush autherized dealerships through out the country. All got the door jam serial number sticker.
The Stage 2 is not just the aero package and exhaust, but the suspension as well. The basic package was Roush specific Bilstein shocks/struts, Roush springs, sway bars and control arms.
There were lots of options for the S2 as well. Many of them also opted for the brake package as well. 13" at all four corners. The calipers are the same as the Cobra units from PBR, rotors are Baer slotted/cross drilled, and SS lines. There was a Roush composite cold air intake option many got as well.
S2 cars also had the interior option: Roush specific leather seats, carbon fiber dash trim, shifter options, floor mats etc...