It wasn't that important to me, as I'm playing on gigantic map size
African slaves have a base price of 100, increasing by 50 each time you buy. Colonists have a base price of 500, so they're as expensive after you buy 8 slaves. Can be great to jumpstart your colonies, seems in line with how the Caribbean developed. But it's not doable to populate dozens of cities.
Apart from that, Africa has the same tax rate as Europe. Some prices are slightly different, but they're in general worse to sell than in Europe.
Only smugglers and pirate ships can go to Port Royal. These aren't cheap, so you can't use it in the early game. And they only have 2 cargo slots. Port Royal has a fixed 20% tax, but Europe can get 30% tax cap, if you improve relations with the king. So I don't bother with smuggling