https://www.revolutionturbo.com/
I talked to revolution turbo they quoted me at $1500 for a large turbine and compressor wheels.. 550whp. Close to PS2 with out porting the manifold.
$3500 for a ball bearing turbo capable or 600 whp.
Steam seems like a great deal
from what i understand though its only a 500 RPM difference in spool.