Bull. shit. Maybe that shack cost $20K, but not the land and septic system. Septic system alone is $25K.
A mini split AC would cool that shack for $800.
I looked into it once. Its Kore complicated than that. Wood on metal sweats and wicks, so then you gel mold. So you need to spray foam it also, making sure wood doesn’t touch the spray foam. And so on.