Yes. That is what they were arguing about.
Googling Kettell & Colwell produces limited data, though it appears both publications are still available, for about $20 each.
You can view them for free online:
Bottom line is, I'm not inclined to believe that Southern slave-masters were in any way being "ripped off" by Northern shippers & business interests, certainly in no way comparable to the degree of rip-off of slaves themselves!
I agree. There was less realization of that at the time, but people weren't entirely unaware of what was going on. On top of that, Kettell, a New York City financial journalist drastically undervalued the services that his city and region provided to the cotton planters. Apparently, he was a Democrat and at the time that meant catering to Southern slaveholding interests and telling them what they wanted to hear.