Looking to move to Northern California - cheapest cost of living city/town between bay area and Napa area?

Vallejo would be a good choice if you move to a good neighborhood. Also American Canyon which is between Vallejo and Napa is great too. Now Napa is fantastic, but your commute would be at least 1 hour from there. Like the other answer Petaluma might do for ya too. It is a nice safe town just a little north of Marin county. BTW, Marin county is just too darn expensive.