My for instance I'm only talking about Centrifugal Blowers. PD have a lot of tech and are pricey, no denying that. Keep in mind below are still retail prices.
Nice older styled oil cooled non-intercooled Paxton kit for Rustang $2500: http://www.ebay.com/itm/PAXTON-NOVI-...00e97f&vxp=mtr
Novi 1200 non-intercooled Kit for Rustang 4.6 mod motor $4255:
Novi 1500 non-intercooled kit for Rustang carbed $4000k:
Intercooler with piping and BOV for anything, universal crap $300:
Finally for a tuner kit
if you could source out mounting brackets and pulley's and using intercooler you would need the head unit, and I've seen some V3's as low as $1300 new:
Vortech V3 $1700:
Or Procharger P-1SC for $2300:
I just can't figure how to get the brackets
Blower V3 $1700+intercooler $300+ brackets and pullies ($500 guess)= $2500
I would say demand definitely drives prices.