The upfront costs of a K-swap almost doesn't seem worth it in an S2000. You can spend close to $10k to do it right before you ever even throw in a power adder to make big numbers. Or you can just spend $10k on a supercharger, a beefed up diff, and a clutch and have a reliable 400hp.
I've crunched the numbers over and over. I've decided if my F22C ever donates a rod to the SpaceX program, I'll go K.
It's the same for most other K-swaps. I have lots of the parts to do it on a Miata for champcar and we are looking at $8000 just in swap parts and a junkyard accord K24Z.