There is a community college in Napa that has a very good cooking program. Outside of their regular 1-year cooking program, they offer short classes on a range of subjects to the community. The bonus is that some of the instructors there are also instructors at the CIA (the 2 schools have a friendly relationship). These classes won't be as advanced as the ones offered at the CIA, but you can get some great deals. I took a one night cheese class for about $45. The instructor is well known in that area as a cheese guru and we were able to sample 20-30 of the most amazing cheeses I have ever tried in my life. I learned a lot even though it was a short class.
The class schedule is posted online, so you should be able to find it with a quick search on google, but as I remember the best classes filled up fast.
The only other thing in the valley I am aware of are the classes put on at the wineries, but these are more for entertainment and won't offer you much that is new.