I have trouble understanding the economics of slavery. It seems that if you want to have a slave worker, you have to not only put down a sizable initial investment, but then you also have to spend enough on that person's food, shelter, and medical care to ensure that they remain healthy. Even if owners weren't required to provide medical care for their slaves, failure to do so would cost them their investment.
By contrast, the only expense involved with taking on an immigrant laborer was putting up a shingle saying "WORKERS WANTED". There were enough immigrants seeking work that no investment was required. If a an employer didn't give a worker enough money for him to stay healthy, the resulting sickness would be no particular loss to the employer--he could simply get rid of the sick worker and hire a replacement.
Why did the South use slaves, then, rather than simply trying to attract immigrant laborers (who would seem, economically, to offer a better deal)?
The north had no need for the commodity, the buying and selling and propagation of slaves.
Look at some types of commodities currently addressed as a financial activity on the stock market...
The way slaves were marketed yesteryear seemed goofy to the North and to us today...imagine what some in the world think of trading pork bellies on the open market...
Here's my take on the situation.
By the time of the Civil War, the South was an impoverished area with an enormous "installed base" of slaves. They didn't necessarily have the money to pay immigrant workers, the best medicine was crude at best and the slaves built their own shelter out of local materials. Food was procured as part of plantation production. Slaves were thought to be a fungible; when one got sick, it was no matter, they'd breed up more soon enough. (Note that this was the slavemasters' general line of thought in the era, not mine.) The slaves were "free" in the thought of the people of the area and time. Remember, the big plantations didn't have to pay to obtain slaves, since they were already there.
This is because the South, in general, decided to not join the industrial revolution, stayed with agricultural production and got left behind when the economic train left the station. After the war, the South (and the rest of the country) did come around to the way of thinking that you describe. There is the famous plutocrat quote along the lines of "Why should we want slaves? An Irishman is so much cheaper, and you can fire him when he becomes too ill to work." Same thing with the Chinese immigrants.
It made sense to the people in that place at that time; it doesn't make sense to us now, when the average educational level is such that the significant majority of people actually understand the basic economics of labor. Which, by the way, is something that you didn't get in schools that "just taught the three 'R's", which was the basic educational system of the era.
Why do people buy stock or land? Slaves were also an investment. They were a commodity where the demand was high and the supply was kept artifically tight because of bans on imports. On larger plantations the value of the slaves exceeded the value of the land and buildings. Put two slaves together and they could crank out little dividends that might be worth $1000 each or more.
As far as upkeep went, there wasn't much to it. Most food for slaves was grown on the plantation so there wasn't much outlay there. Shelter was rudimentary, clothing was minimal, and health care wasn't much of an outlay either. In return you had labor for life. You didn't have to worry about whether hired labor would be available when you needed it, or whether you would have to outbid someone else for the hired help. Slavery was a pillar of Southern society and not an institution they were about to give up lightly.
It was even worse than that, because slavemasters needed to spend money on tools that sharecroppers would have paid for themselves, overseers to ensure that work was being done, and the price of caring for slaves who were too old or injured to work.