The cost is insignificant.

I have monitoring on all the phases on my house (in Sweden) and I can charge two electric cars, run the heating in winter, run the washer and drier and cook with two ovens a microwave and the induction hob at the same time and everything just works.

Things on three phase in my home: swimming pool, sauna, induction hob, electric car chargers, heating system and I have sockets to plug-in welding and other power hungry equipment. The rest is split on the phases. I can’t remember whether my solar system supplies on three phases or not but I think it does.