The sentence is grammatically correct. It follows the basic structure "[Noun A] is as [adjective] as [Noun B]" but also includes another noun after the adjective, [Category X], which tells you that Noun A and B are both in "Category X." A simple example is "John is as smart a student as Jerry": John and Jerry are both students and they are equally smart. In the case of your sentence, Rockefeller is saying that coffee, sugar, and personal skills (like "dealing with people" or "speaking English") are commodities (things you can buy). You can see other examples here: http://forum.wordreference.com/showthread.php?t=1792139 I hope that helps!

The sentence is grammatically correct. What Rockefeller is saying is that the ability to deal with people is valuable, like the physical commodities that made him wealthy.

"as purchasable a commodity as sugar or coffee" means that just like you can buy sugar or coffee, you can also buy the ability to deal with people. John D says that he will pay more for (people who have) the ability to deal with people than he would for anything else.