We're on heavy clay and the farmers around us growing wheat to feed their stock reckon on 3 tonnes an acre without any fertiliser other than FYM. You have to factor in machinery or contractor costs, sprays if it's not organic, time spent weeding ..... Wheat on its own may not be the optimum diet for layers but what else you could grow would depend on soil, climate, height above sea level, how far North you are, etc.