I booked a day of coordinator! Mainly because we needed help with setup and tear down, and also because we didn't want to spend our time on the day of the wedding running around, coordinating other vendors, answering questions, etc. I'm not sure of the average cost in California, but check out wedding planning vendors under the Vendor tab here on Wedding Wire! Alternatively, if you're in any Facebook groups for local weddings, you could put a post out, asking for day of coordinator suggestions. Vendors are often in those groups, so list your budget for one, along with your wedding date and general location and what specific services you're looking for, and vendors who feel that they would be a good fit will reply.
I just booked a DOC for the San Diego area! She specializes specifically in DOC and doesn't have a full service planning option, and her prices are superrrr reasonable. I received proposals from 3 different planning companies ranging from $1000 (<50 guests, no assistant) - $2795 (2 dedicated planners, design coordination, style consultation). I found all of them on The Knot by filtering the wedding planning section by filtering "Planning Services" for "Day of Coordination"
We booked a DOC because I need help getting our rentals set up and picked back up, I wanted a recommended vendor list, and because I wanted to feel like a guest at my own wedding.