FYI: If you're talking about Nippon aka "No Name" - it closed.
I don't generally seach out sushi based on price but I do find the sushi at the two grocery stores in Japantown to be very reasonable.
I like places like K's Kitchen that offer more than just sushi. Mostly because I can augment the meal with less expensive side dishes and then splurge on just the very best fish.
314 Church St, San Francisco, CA
757 Monterey Blvd, San Francisco, CA