Mom and pop markets are a staple of the central city, and they tend to be more expensive than supermarkets. You pay extra for the convenience and the smaller market’s lower wholesale purchasing power. So, how do you explain ethnic mom and pop markets, which often sell groceries the cheapest? Take the Asian Food Center. Fresh prawns (actually thawed, the standard practice of seafood purveyors) are sold for dollars less per pound than at the supermarkets or specialty grocers. Live lobsters and crabs also are available on the cheap. The produce section has additional deals, such as a big, fat bunch of cilantro for 49 cents. Then there is the stuff you can’t find at a regular market, such as the hot Indonesian ginger chews called Ting Ting Jahe, for 39 cents. The dollar may have taken a pounding lately in world markets, but a buck still goes a long way in the ethnic markets. 1301 Broadway in Sacramento.