Not just cheap though - near zero. If we have an infinite tap of it, we can afford to waste a lot of it in the process of delivering it. The inefficient becomes efficient when you plug in infinities and zeroes
Energy costs might drop an order of magnitude, which is significant, but isn't going to cause any sort of systemic change.
See: https://reneweconomy.com.au/why-god-parity-will-be-the-end-o...