You know, that’s a good question. I don’t know if modern humans will ever figure out exactly how the pyramids were constructed. There are so many theories as to know it was done—from wind power, to laborers, to slaves. The possibilities are endless.
Personally, the most creditable one is laborers. Egyptologists found so much evidence that laborers would devote a small segment of their life to help construct tombs, temples, and monuments. The laborers were well cared for in exchange for their skills. Hollywood defiantly made people believe that Egyptians were ruthless monsters who used slaves—it’s not true.
Also, you had mentioned abut the cost of the pyramid (7.5 million). I personally think this fiqure would be wrong due to stone crafting, engineers, materials, and construction. Very interesting number though, would love to hear where you got that figure.