The studs themself are cheap. But come in parts
*The stud itself
*The top bolt
*The springy washer
*The flat washer
By memory it was around $6 for each stud set all up.
The replacement manifold was about $140 Genuine Nissan also.
Your local Nissan dealer can get them in no probs.
If you're doing it yourself, i gaurantee at least ONE will snap off, so have a drill and an easy-out handy, as you're gonna need it! Took me about 2 days to replace 3 of my broken ones.
I also used ultra-heat gasket sealant aswell, so now it's a helluva lot stronger than before!