The price for a PST with steel yokes and CF shaft is around 500 - 550. If you go with T-6061 aluminum yokes, like I did, the price shoots up to nearly $800. Of course, aluminum shafts are cheaper.
The FMS driveshaft will fit on some IRS Cobras due to factory tolerences being slightly different. If it fits, it will be tight. Otherwise, you have to go with the overpriced Griggs unit or the expensive carbon fibre.