The cost of corn stover (leaves and stalk) is $40-$80 including transportation it's about $100 per ton [1].

So, that's $90 trillion at US biomass production prices (assuming that much biomass was available) or 1.2x world annual gross world product [2].

Still $90 trillion seems like a lot.

[1] https://www.extension.purdue.edu/extmedia/EC/RE-3-W.pdf [2] https://en.wikipedia.org/wiki/Gross_world_product