The ALLEN kits goes for $3,900 for the 6psi kit (about the same price as the non-intercooled KB), to $4,200 for the 9psi kit (about $800 less than the intercooled KB). Thier site lists them as more, but I believe Stangnet members are entiltled to a 10% discount off of retail. THe nice thing about the Allen kits is that they all come equipped with intercoolers as standard equipment. Which is kinda nice for regulating power levels on a hot day, or after hot lapping your car at the track. As for power....they'll hold their own against either of the other blowers mention up till about 375-400rwhp. But after that, it's pretty hard to compete with the lower discharge temperatures and sheer size difference of the big Twin Screws and Centrifugals.
Either way though, 400rwhp is nothing to sneeze at. It's enough to get your car into the 11's, which is faster than most ever see.