(How to make a supercharger cost $21,000...)

What you're talking about is an axial flow compressor. The compressor part of a turbocharger is a radial flow (actually mixed-flow) compressor. That's probably more compact & cheaper, & more effective for a car. But most superchargers are more like positive-displacement pumps, although that's sorta misleading 'cause air is compressible.

Early jet engines (Whittle, Junkers) used radial flow compressors, but when they started to get bigger & more powerful, they had to give up the advantage of 'centrifugal force', in favor of a skinnier design. You probably know all about how critical the tip clearances are, but in the USAF maybe you never knew how expensive that stuff is??