I live in Sonoma County, about an hour away from St. Helena. I haven't gone there often; mostly I've passed through on my way to other places like Clearlake. It's north of Napa, and while that whole valley is kinda pricey, I'm not sure if St. Helena is more or less expensive than Napa – probably depends on the neighborhood. I think it gets pretty warm over there, but it's a good location. Not too long to San Francisco or Sacramento. I think if you can get a good job there, it would be a nice place to live.
Hope that helps some!