The East Bay includes Piedmont ("Rich Oakland"), Orinda/Lafayette/Moraga, Danville, Alamo, and others--so plenty of expensive zip codes, but relatively speaking, the cities in the east bay have a lower price point than the cities on the Peninsula or in the Silicon Valley--as shown in that chart above. If you include all 9 counties considered in the Bay Area, no, Alameda County isn't the "low cost" area, but of the counties that are right on the Bay (as opposed to the Delta), Marin, San Mateo, and Santa Clara are more expensive than San Francisco, then Alameda, then Contra Costa.