how does mac sell its operating system?
Either as part of the system when purchased, as a single license, or as a family pack (five licenses.)
Unlike Windows, Apple does not have different levels of it’s OS. There’s not a home, ultimate, etc.
For Snow Leopard, the pricing was $29 for a single or $49 for a family pack. On a lot of non Apple sites on the web it said the license was for upgrading of Leopard only, but when I bought it, it didn’t say that anywhere on the packaging, and I didn’t find it anywhere on the license agreement, although I didn’t scroll the entire thing.
I bought OS X.6 Snow Leopard in a family pack of Five licenses for $49. It's still available at that price.