If you go a little West to Mission Bay, there is a combination sushi bar/bait shop right on the beach, and its much less expensive than the fancy places if you're okay with plastic plates and paper napkins.  The sushi is never more than 24 hours old, because after that, they lower the price even more and sell it as bait to the local fishermen.  Once you get in the area, ask around.  All the locals know about it.  

IMHO there are two very good places to try.

Harney Sushi is in nearby Old Town at 3964 Harney Street.

However, my fav is Sushi Ota at 4529 Mission Bay Drive in PB.

Why not try them both?