Maybe I don't understand the math but overtime is 1.5x wage. So to get around it farmers hire 2x workers at 1x wage? It seems that hiring more workers should be more expensive.
(100 x 40 x 20) + (100 x 30 x 30) = 170,000
200 workers working 35 hours a week at 20/hour:
200 x 35 x 20 = 140,000