Well with both of our cars charging it hasn't cost us a single cent that I can tell, but we have been charging cars here since 2011 and have 12.5K of solar on the house. With three 3ton heat pumps (2 big trane units and a Daikin mini-split with 3 heads), a 2HP inverter swimming pool pump running 4 hours a day and electric clothes dryer and all the other electrical loads our total bill last year was under $600, which in AZ is pretty much unheard of without solar. We have mostly LED lighting and are near our complete conversion as the CFLs die. There are lots of parasitic loads like Dish boxes, 2 Apple mac minis, HP printer, network router, phone charging, 5 ring cameras, etc etc.
I like driving for free, the solar has been long paid for and met its ROI many years ago.