Southern Cali resident here: I got a mini split system installed a couple years back, and last year's eye-popping surprise gas bill inspired me to start running it backward for heat instead of using the furnace.

Pricewise, it's actually a wash. My electric bill went up by about $100 a month, whereas during the winter my gas bill was running about $100 a month to run the furnace (aside from that one random $600 bill one month last year that inspired this change). I've been using the mini split all winter and it's been great.