Source: I dated a literal farmer's daughter and talked with him a fair bit about the economics of his farm (corn, soybeans, and dairy, plus associated by-products) and farms larger than his. He was sharp on the numbers in addition to being sharp on the biology.

The concept of self-sustaining farming and ranching is as old as dirt itself, with various implementations including crop rotation or fallow fields, but it typically means that the are of land dedicated to a staple crop (such as oats or wheat for the exemplar GM) drops dramatically, as would the profits.

Nothing in the linked literature disagrees with this notion or comments on the different costs (other than the grants for a farm that's trying it).