The cost of achieving a 90% clean grid using today’s technology is approximately zero. 
And this excludes the external costs of fossil fuels: climate impacts, air pollution, geopolitical instability. 
https://www.theclimatebrink.com/p/is-renewable-energy-cheaper-than?utm_source=cbnewsletter&utm_medium=email&utm_term=2024-03-12&utm_campaign=Daily+Briefing+12+03+2024