>I'm not sure if slaves were this expensive back in ancient Greek or Roman times, but I suspect it probably wasn't that different.
The price fluctuated heavily. After a successful conquest slaves were way more affordable. Generally, a lot of people were able to afford slaves, so it was cheaper on average too. It was also place-dependent, compare for example Athens where roughly half of the population was free, and Sparta, where most of the population was enslaved.
And of course even when slaves were expensive, most economically important labor was done by them anyway.
If the slaves in Sparta far outnumbered the native population of Spartans, what exactly kept them from revolting and taking over? Was it just because the Spartans were all trained as warriors?
The price fluctuated heavily. After a successful conquest slaves were way more affordable. Generally, a lot of people were able to afford slaves, so it was cheaper on average too. It was also place-dependent, compare for example Athens where roughly half of the population was free, and Sparta, where most of the population was enslaved.
And of course even when slaves were expensive, most economically important labor was done by them anyway.