Really, it depends on the barn. In like, San Juan capistrano, (big time horse country), you have these fancy show barns that are like 500-800 a month, stall board with turnout, feed, blanketing, or you have the farms that have outside board, covered with feed. I'm in central california, but my trainer used to work down there and we go to shows with other barns. Her mom's farm has outside board, covered, with hay and grain for $12 a day. Really, ask around, and find a place that suits you: what your horse needs, places to ride, a trainer if you need, and what you want to see in a facility. These show barns have gorgeous barns, arenas, and trails, as well as are close to big show venues, like Galway Downs, Copper Meadows, and such.
Hope this helps!