Rubbish, the truth is, when a Southern planter sold his cotton to "factors", he received full market value for his cotton, then & there.
"Factors" then transported the cotton to, eventually, a sea port like New Orleans where it was sold again at market prices there.
Most cotton then shipped directly to ports in Britain & France, where it was again sold, each time at then available market prices.
If the Southern planter decided to keep ownership of his crop, and himself transport it to a port and then Europe, he would indeed make much more in gross revenues.
But he would then himself have to pay all the transportation, shipping & warehousing costs, meaning there was likely a "break even point" of quantity below which it was no longer profitable for the Southern planter to himself pay for transportation & sales overseas.
Couldn't get any ships. Wasn't allowed to use Foreign ships and had to go through the Northeastern monopoly where they priced the carrying fees just beneath the cost of all the fines and penalties he would pay from trying to use foreign ships or crew.
It was a great little racket for the North, and it was enforced by the Federal government. Kinda like all those "vaccines" that are made in Massachusetts, New York and New Jersey.
I hear Pfizer made 90 billion. Best year they ever had.