Thanks Vytas! PM sent.
Thanks for the feedback chriswtx and SCS2k.
This seems like another case of honda needlessly jacking up the price of NSX parts. I did some more digging and the S2k OEM cap was $10, accord was $6, and civic was $5. In comparison, the NSX cap was $21 with club discount and $28 at the dealer! The fact that they are interchangeable only makes it worse. At that price, you could get a billet aluminum one as suggested.