Taking the (shamefully low) minimum wage in the USA of $7.25/hr and assuming your employees work 40-hour weeks with 2 weeks vacation, that's $14,500 (again, shamefully low but let's roll with it).

Ten thousand of those workers costs you $145 million per year, and for twenty years that's some $2.9 Billion.

It's pretty obvious we could build a pyramid, which is basically just a hill of rubble with worked sides, for a lot less today if we only needed it to stay up for a few years.