With all the caveats slavery was evil .etc. my comment would be: In today’s dollars a slave was about $100,000. Most owners bought insurance on their slaves also. A huge investment. Not likely to purposely abuse them.
I never heard about insurance on slaves.
I suspect that your slave price in today's dollars is too high, but I agree that it made sense to treat your slaves well. We visited an old plantation outside of Charleston, SC -- the staff there pointed out that if you treated your slaves badly, you might end up some night with some of your farm buildings on fire.
After he had been in office for a while, Lincoln floated an idea that the government would purchase slaves in Delaware for $400 [Link]. On the other hand, the average price for slaves from 1856 to 1860 was about $1,658 [Source]. Using Inflation Calculator, that $1,658 translates to about $39,000 to $40,000. Using Inflation Calculator Number 2, the price is about $44,000. The modern equivalent of Lincoln's price would be a quarter of those values.
The inflation calculations by these sites depend on how they calculated inflation in the first place. If they leave out key factors like fuel or food like the Core CPI does, they may undercalculate the modern equivalent price.