It sounds like you are asking "is there an economy of scale?" to burying power lines. Or "is there a learning curve that will drive the costs down?", like for solar.

The answer seems to be 'no'. Digging and burying pipes is something we've been doing on a massive scale for hundreds of years and there's no reason to believe more volume will improve the economics. It's probably getting worse since new development means more roads to dig up and more structures to plan around.