OPERATIONAL COSTINGS
Using a net labor productivity improvement factor of 1.37 (over manual or traditional techniques) the thresher should 'save' 0.37 man-days per operator-day for 6 operators for up to 30 days per growing season per year.
Using a net labor productivity improvement factor of 1.3 to 1.7 (over manual or traditional techniques) the mill should 'save' 0.3 to 0.7 man-days or women-days per operator-day for 4 operators for up to 320 effective days per year.
If we price labor at US$ 1 per man-day then the thresher can 'save' US$ 66 per growing season, compared with its cost of US$ 520 - not actually very impressive.... and taking 8 years to pay itself off if a zero rate of interest can be levied (an unlikely situation).
The mill can 'save' US$ 400 to US$ 900 per year, disregarding plate replacement costs (unknown or unresearched) and maintenance or repair costs - a much more impressive sum.
Coming from another angle, compare the thresher cost with the value of the grain which can be processed - 22.5 tonnes per growing season (and therefore probably per year) - @ US$ 0.100 per kg is US$ 2250 grain value per year; @US$ 0.200 per kg is US$ 4500 grain value per year. Compare with a machine cost of US$ 520 and a probable effective thresher lifetime of 5 to 20 years - and it doesnt look too bad. If it were possible to extend threshed quantity by working 12 to 24 hours per day instead of 6-8 by using 12 to 24 operators working in rotas, then the economics would look better.
Coming from a 3rd angle, for milling compare with a commercial costing of US$ 0.040 per kg milled. If one can mill 40 kg per operator per day (1 kWh mechanical energy per operator per day) then that corresponds to US$ 1.60 per operator per day value added, giving US$ 0.60 per operator per day available to amortise the mill and drive mechanism. Amortisation would take about 200 days, or 8 months to pay off the complete machine (including thresher).