Let's say that I'm a slave owner that purchases 50 slaves. I tell each and every slave that to free themselves, they have to work enough to pay off their purchase and another slave purchase so that more slaves can be bought and freed. Thus, 50 slaves work to pay off themselves and another so that now I can buy 100 slaves. This goes on and on. Besides the huge costs for food and shelter, were there any people in history that did something similar? Even if it took many many years, has this ever happened?
I've never read of anything like that. Individual enslavers might permit slaves to earn money by selling the products of their garden plots or retaining some of the fee from renting their labor out, which could potentially mean cash for freedom down the road, but a plan for a steady stream of freedpeople coming out the end is anathema to the whole idea of slavery in the antebellum US. Rather we see extensive moves to restrict freedpeople to near-slavery and occasional efforts toward outright re-enslaving them.
There are cases of people promising to free slaves in exchange for money down the road, but those promises were almost impossible to enforce if the enslaver (or heirs) felt differently then. None of them that I know of involve a plan to use the proceeds to buy more slaves. Rather slaves are mostly freed as a special reward, a bequest in a will, or because the enslaver wants to be quit of slavery entirely.