The emergence of Masa as the madly expensive sushi bar of the moment has taken the thrill out of riding a drab office elevator to this dowdy, hidden dining room. Japanese businessmen and Wall Street bonus babies still flock here, though, for omakase (chef’s choice) dinners, featuring rare cuts like katsuo (skipjack bonito) and shima-aji (striped horse mackerel). You better pray that your platinum card is up to the job, because there’s no set menu or even a price list. Masa’s $300 prix fixe seems tame compared to the guessing system at Kuruma: You’ll only be able to surmise from the unitemized bill that your orgasmic roll of o-toro (the highest grade of fatty tuna), which was topped with Iranian caviar, ran $200 for four bites. Kuruma’s fish soar, but the restaurant’s exorbitant pricing and lack of ambience are definite sinkers.