I'm getting my manifold made at a place called exotic exhaust.
The manifold itself is going to cost $500 and its also gonna cost me $250 for a 3" dump pipe.
I know there is a mob in Melbourne called Ridgecrest that specialize in metal gaskets and forged conrods, etc. I've sent them an e-mail about a gasket for an 18rg, but I've yet to get a reply. (I only sent it on friday)
I'm not sure what the gasket will be worth though.