Professional installation of the Mitsubishi mini-split will be at least $2000, most likely a lot more in the Bay area. Given the size, limited use of the room, and the mild climate, the mini split cost is not worth it in my opinion.

The OP's description of the equipment suggests he will be buying it himself directly and then asking an HVAC contractor as a separate matter to install it. My experience suggests that the better HVAC contractors won't have any interest in doing such a job. Zero. They want work where the install, maintenance, and warranty service (if needed) involves equipment they've sold. A one-off "come install this system I bought directly and then go away" won't be a something they want to do. The building trades are booming here - someone with time available and an interest to do this isn't someone you'd want to hire.

If you're thinking of a window AC, get a window heat pump instead. It will provide heating and cooling. If you want a nicer appearance, unless this is an out building, have it mounted in the wall and not in a window. Or, get a PTAC heat pump, like in motel rooms. PG+E will be happy with you.

Ouch...didn't think it would cost that much. I don't need to purchase it myself, but I also don't want a $5000 price tag. I'll look into the PTAC and window heat pumps. Thanks much.

If you want a minisplit system, forget about buying it directly. Call a few HVAC companies and get quotes to provide equipment and installation. You're talking about something the size of a two car garage, if well insulated, a smaller system should suffice. But they are pricey. They are getting popular in our area for additions, converted interior spaces, and rooms where an existing HVAC system doesn't provide enough airflow. (I'm in the Bay Area too).

No matter what equipment approach you take, you'll probably need the services of an electrician too, to provide a circuit with more oomph than a standard 15 amp 120v line. Certainly for a minisplit, you'll need 220/240. As would be the case for a large enough AC or heat pump unit.