One thing is pretty sure - we need to overbuild solar and wind. The total annual energy consumption in the US is around 15 PWh. Notably, the per capita energy consumption has essentially remained flat for four decades now.
This energy consumption thus translates to an averaged power requirement of 4TW. Notably, while peaks are local, however nationally, extremes are not that higher than average. The average capacity factor is a third for renewables, so 12TW of nameplate renewable capacity is enough for the vast majority of the time - to power the entire nation's complete energy requirements through renewables.
Let's go with a 50-25-25 mix of solar-onshore-offshore wind. Thus solar nameplate needs to be 6TW, and both onshore and offshore wind needs to have 3TW nameplate capacity installed each. Solar PV generates 10W per square foot. That's 22,000 square miles. A lot of that can come from rooftop solar. Onshore wind turbines are 2.5MW each, which translates to 1.2 million turbines, while with the offshore turbine designs that this article shows - this is 200k turbines. The cost of such turbines (onshore+offshore) with installation would come to 9 trillion USD. Solar would cost a similar amount. Battery costs for storing 96TWh (a day's worth of energy consumption - averaged) would be 10 trillion dollars more.
Thus, building the nameplate capacity for the entire US to be powered by renewables is approximately 30 trillion dollars, where the GND price tag originated. However, all of these are at current solar/wind/storage prices. Each of those three is falling, and if the market becomes this big, economies of scale will drive costs down further.