I don't know why it would be cheaper to purchase and maintain highly complex machines rather than provide food and clothing to a slave. It's not like either the food, clothing or shelter is of the highest quality. Human beings in the real world are more resilient than you'd think. Especially when you get into pictures of starving people in Africa as the result of persecution, there are pictures of people on their feet marching, when they are skin and bones to the point that they don't even look like they should be alive. Star Wars is not so graphic. For the cost of purchasing a car and keeping it maintained, I could probably feed, shelter and clothe several people. They would enjoy the crappiest quality of living, but since when is being a slave luxurious? It seems more like a prestige thing in the Star Wars universe. I have command over another person's life, they are my property, that conveys greater power than buying some droid that is programmed to obey. A lot of money was tied up in slaves in the American South. They by no means enjoyed luxury and a stern slave driver was not going to tolerate disobedience from something he viewed as his property, just as many dog owners will not tolerate a dog that would bite them. But my understanding is that the harshness is often exaggerated. It's not like a slave master would intentionally work his slaves to death in the field. He spent an incredibly large amount of money for that slave and he only gets that money back if the slave is productive, working the fields (i.e. alive). With Jabba the slaves just seem like servants and symbols of status. His money largely derives from smuggling and other illegal activities. Oola isn't out there making any real profit for Jabba. She just dances for him, is implied to be used in some kind of sexual manner, and is otherwise expendable to him. In instances like Wookiees. As someone else said it's largely a scare tactic, I think. Make an example of them. Maybe droids would be more efficient, but having a bunch of droids in roles of servitude is not as intimidating as Palpatine forcing opponents into servitude.