I am sure that many, even most slaves were in fact paid enough to stay alive (more specifically, they were probably fed and housed on the job); just not enough to stay alive in what I would consider reasonable comfort. And, in at least some cases, not at all once they were too old to work. (Some would have, I'm sure, been brought in healthy and than starved and died, through sheer incompetence on the part of the owner if nothing else; but those would have been the exception rather than the rule).