Sushi rice in a restaurant will be just the glutinous rice mixed with rice vinegar. Nori, soy, wasabi and pickled ginger are free so the only thing you have to allow for is if you are having the fish as a HEX, or in some california rolls they have sesame seeds and mayo.
Have it on a EE day and it is great. I ate a TON of it on Saturday at a lovely restaurant in Manchester. I also make my own occasionally as then I know exactly what is going into it.
They have started selling the uncooked rice, nori, etc at larger supermarkets (My Tesco's have them) or you could find a nice oriental shop? My favourite food ever
xx