Via Tom Philpott at Gristmill, Gourmet has an article describing a 4,000 acre family farm in Walworth County, SD. It's been in the family for generations, since 1880's. Not clear whether the family owns the 4,000 acres free and clear, but if they do it's a key to their survival. I think it's generally true that farm owner/operators, with luck and good management, can survive the bad times and prosper in the good times even if, as here, they occupy a niche market (organic wheat). As long as cash flow is positive (meaning no rent payments or mortgage payments) you can survive. (That's how my parents farmed on an uneconomic dairy/poultry farm.) Of course, if you're young you need to expand your acreage (to support the bigger and better equipment), so being able to buy wisely and timely is key. (Or else, you spend your winters rebuilding used stuff.) If you're old, you just carry on living off the depreciation of your old equipment and hope it lasts as long as you.
Without knowing more about the area and the economics, I wouldn't commit to the idea that the Stiegelmeiers are a viable example of how the Great Plains might be farmed. (A concept both Philpott and Prof. Dobbs, ag economist, float.)