acre
This would obviously depend on where in Louisiana you are buying this acre of land. An acre in New Orleans' Garden District is worth more than an acre at the Arkansas border for example.
2 cents per acre
It is usually called, "a quarter acre" or "one quarter acre".
$15 million (3 cents per acre)
That it was purchased for a penny an acre.
Less than 3 cents per acre.
around 2 cents per acre
As a price per acre, the Gadsden Purchase was 53 cents per acre. As an aside, this was was 18 times the price of the Louisiana Purchase.
Louisiana Purchase
It is 1 acre.
$15 million or 3,750,00 francs was the price for the Louisiana Territory. The 1803 agreement was known as the Louisiana Purchase, whereby the French gave up their claims to the western Mississippi valley.
$15 million, which was like 3 cents an acre at the time