Costly, yes. But do those costs out-weigh the immediate benefits of slave ownership? Probably not.
I have a hard time thinking slave-owners were hurt by slavery; they made out like bandits, but their gains don't counter all the harm done to those enslaved.
That's a more difficult question to answer. Slaves are only good for the lowest menial labor, such as picking cotton. Up until the introduction of the cotton gin, slavery was dying out in the US because it was unprofitable. The cotton gin made slavery profitable again, but it was again dying out by the time of the Civil War. One of the causes of the Civil War was the southern states trying to erect trade barriers to protect the economics of the slave plantations.
Businesses run on slave labor just could not compete with those run with free labor.
(For example, it was illegal in the slave states to teach slaves to read, and any slave who could read would do well to conceal the skill. The southerners were fearful of an educated slave, because that made them more dangerous. But an illiterate slave was also less useful as a worker.)
Costly, yes. But do those costs out-weigh the immediate benefits of slave ownership? Probably not.
I have a hard time thinking slave-owners were hurt by slavery; they made out like bandits, but their gains don't counter all the harm done to those enslaved.