40 minutes to Cupertino with no traffic on I-280.
37 minutes to Palo Alto Square.
A mere 30 minutes (no traffic) to El Camino in Redwood City, but does Redwood City even count as Silicon Valley? It's certainly on the edge.
40 minutes to Mission Street in SF.
All these numbers are Google's estimates and are subject to going way up when traffic is happening.
Though I've never looked, my hypothesis is that Half Moon Bay is not substantially cheaper for rent than either SF or the Valley. There are fewer people, but there is also a smaller supply of housing, and the relative size of the rental market is smaller.
And, in the absence of a tremendous bargain on rent or an irrepressible love of daily walks along foggy Pacific beaches, I'd rather live right next door to something. Live next door to the night life, or live next door to work, but don't commute 40 minutes to everything.