I live in FL, which is the opposite side of the country, but I hear living costs in CA are much higher, so I'm not jealous, LOL. Here's how it breaks down:
-My TB himself cost 500 dollars to buy, but then I paid for him to stay on the old owners property for a month, so the cost of that was like an extra 150.
-425 a month for board (but I know bales of hay here cost like 7 or 8 dollars a bale...my TB eats like 8 or 9 bales of hay a month by himself, and grain is 25 dollars a bag, so thats 100 dollars a month)
-10-15 dollars every other month for wormer
-35 dollars every six weeks for a hoof trim, but it was 80 when he was getting shod in the front
-his tack set cost me 300 dollars used, thats a saddle, headstall, reins and a breast collar, I bought the bit separate for 25, and then a hackamore for another 25, and then new reins for ten.
-his vaccinations are relatively cheap, something like 120 bucks for everything he needs in the spring...it goes down to like 40 in the fall, because I do the vaccs myself then.
-don't forget to factor in an emergency fund (or a credit card payment, lol) and also some money to play with; you might want to go to a clinic here or there, or maybe hire a trainer or take lessons or something.