If so, what are the prices? Or do you simply look to BoVD or BoED for slavery rules?
Probably on the black market. And as always on black markets, prices will probably be highly variable.
The black market is described in the player's guide (if I am not mistaken).
Even the black markets it would be unlikely, being that Sasserine came out under the rule of a slave nation, they are very against subjugation of others right now. Though there are probably illegal smugglers to the Sea Princes or the Scarlet Brotherhood, both slave nations, that you could trade "goods" with. Though the penalties for getting caught would be severe.
Halber
IIRC, the neogi section in Lords of Madness has some paragraphs about pricing slaves.
In the game I'm running, the purchase of slaves in Sasserine is strictly prohibited. The owning of slaves, however, is perfectly legal.
Its kind of like contributing to the delinquency of minors. If the police catch you in the act of handing alcohol to a minor, you're busted. But if you're sitting in a room with a bunch of smashed underaged kids, but the police didn't actually see you give it to them, you're a-okay.