I am also curious to know what the prices would be with inflation considered. Could slaves only be afforded by modern day millionaires? Or could they also be afforded by a modern day middle class family?
The prices of slaves varied a lot. The price would vary over time. The price would vary across different regions. The price would vary depending on the age sex and condition of the slave.
The skills of the slave were also a factor in the price. Blacksmiths were valuable (+55% over the average slave price), as were carpenters (+45%), and cooks (+20%).
Other factors could lower the price of a slave. Being a known runaway (-60%), being an habitual drunk (-50%)
The average price of a slave in the American South in the first half of the 19th century was about $350. There were two peaks, one in about 1820 and another in about 1838 when prices went much higher. The average price shot up over $450 in 1820 and over $600 in 1838. (It rose steeply again between 1850 and 1860, but this is later than the period you asked about.)
Very young and very old slaves cost much less.
Male slaves in their late teens or early 20s in the "New South" (Western South, such as Louisiana) cost the most (about 25% more than the same male slave of the same age in Virginia, and about 40% more than a female slave of the same age in Virginia. A female slave of that age in the "New South" cost slightly less than a male slave in the "Old South").
Slaves in the prime age group cost considerably more than the average price for a slave (circa twice as much).
Comparing the value of slaves then to the value of slaves today is tricky. There are various ways to try to make the comparison.
If we compare the value of the slave as a worker (the income the owner expected to derive from the slave's labor minus the cost of the slave's upkeep over the expected useful working years for the slave, discounted by the interest rate to reflect that one had to pay for the slave today, but receive the benefits in the future) to today's wages, the average value of a slave between 1800 and 1850 would have been about $80,000.
If we compare the price of a slave to the average income of non-slaves, the "economic status" of owning a slave (or the price of a slave compared to the average income of non-slaves) would have been about $175,000 in today's terms. (The average price of a slave in the first half of the 19th century was about the same as the average price of a house. Houses at that time, however, were generally smaller and less complex than houses today. The average cost of a slave translated into today's values would probably be less than the average price of a house today).
If we look at the average price of a slave adjusted for inflation (by the Consumer Price Index (or various approximations of the CPI for periods when it was not calculated)) the average price for the first half of the 19th century would have been about $8,000.
The price of a slave in today's value was likely somewhere between $8,000 and $175,000 (depending on how you try to translate value). The inflation adjusted price is probably not the best way to look at it, and the price corrected to today's values would probably be considerably higher than $8,000. Even if it was as high as $175,000, however, (or $80,000, which I think is the best approximation) it was still affordable not only by millionaires but by more modestly well off people. About 25% of families in the slave states owned at least one slave.
Possibly the best comparison would be to think of the cost of a slave then as about the same as the cost of a luxury imported car today. However, although the slave would depreciate in value with age (just like the car) the slave would also make the owner money (unlike the car). Although buying a slave might have "cost" about the same then as buying a luxury car today, buying a slave was a much better economic decision and more likely to have been saved up for, borrowed for, and purchased.
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