im no engine guru, but i can assure you, tomei products are worth the coin.I can say this from personal experience.Tomei refers to themselves as the engine specialists and are very respected in the race tracks in japan...
That being said, im sure you could get other similar products to tomei ones for cheaper but id have no idea how they perform other than the nismo ones.
Nismo also has a similar metal gasket to the tomei one and bige had them last time i asked him on a thread on this forum.