Looking for downtown eats not expensive and not Japanese. Looking for something ethnic and interesting.
Cuban? Cuba Central @ 1st/Central
Vietnamese and Chinese are as close as Chinatown. I like Pho 87 on Broadway, but lots of people like Pho 79 as well.
You might also want to try a Farmer's Market. I went to the one on 5th yesterday (it's every Wednesday) and picked up some delicious hummus and taboulie with pita bread for $10. They serve all kinds of food, from rotisserie chicken to peruvian rice plates to bacon-wrapped hot dogs.