Imagine how much more expensive it would be if renewables didn't make up such a big share.

Probably cheaper? Renewables have a big upfront Capex usually financed.

Everything has a big upfront Capex. However you finance it and because renewables are cheap fuel they come out cheap in the long run.

A large part of the Capex of renewables is land costs - which are high, but once you have the land you keep it. This cost is generally all financed as part of the initial build, so in 30 years everything is paid for - but you have to finance to replace only the renewables while keeping the land and so the second round is a lot cheaper.

For fossil fuels the cost in in the fuel, usually.

No, renewables are much cheaper.

Including the cost of the batteries to make it stable over the day? Would need a source for that. My understanding is it comparable at best, but certainly not "much cheaper".