I guess a whole damn lot of those workers - be them slaves or not- did not get any money at all. Currency was a rather new invention by the time that a certain number of pyramids were build already. So I don't really think that one has to break his head with the question of "where the money came from". The "paid" workers would have probably gotten a salary, in its most ancient form, being a block of salt.
But what KevinLancaster said, is also my opinion. Plenty of workers just participated out of religious drive. A belief in an afterlife, coupled with a God-King ho descents to the heavens, probably fueled the idea that if you helped your God-King and then you die, you'ld probably score good points entering the heavens - where your God-King rules eternally.
On topic: Civ did not really help into broadening my knowledge of Ancient Egypt. I was already interested in history before I rolled into Civ, so I already knew a thing or two about them. Granted, I had good teachers, and me following Latin at school with a teacher who was a civilopedia on his own about all things Ancient History, the civilopedia of Civilization only learned me at best 1% of the knowledge I have about them. On the other hand, the differences between the cultures back then was small. The only thing civ-specific was the colour, the name of your leader and the names of your founded towns. And most of that, you could change that too... Aah, the days of the original civ

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I never gotten into civ2, so I can't give an opinion about that, and now I'm stuck at CivIII, because my laptop is not what you might call powerfull.
And while CivIII gives each different tribe a bit more body, with the UU etc, it came also way later in my life. Hence, the civilopedia was a few steps behind on my own RL knowledge gathering. Because by that time, I had done a year of history at university...
The thing is, the evolution of the different tribes in this game tends to not follow earths history at all. This game is far from being a time-machine, as more-often you will re-write history.
I've sent the Greeks into space countless times, the Byzantines dominated the world twice already - but also once achieved victory through carefull diplomacy, the Russians wiped every single civ from the world once, the Celts were just grand by the time the historians were anxious to do something else, etc,etc...
There are no civ-specific sciences, and there's only 5 different building-styles in the game, whom are more region related as something else.
While this game might kindle the flame of interest for history, it certainly is not a valid source... unless offcourse your initial level of historical knowledge is almost down to nothing. Which implies that this player is either very young or not at all that much interested in history.