I created these formulas many years ago while bored in a Trig class. They are based on the values for small medium and large stills from the basic equipment sheet.
output = 7.436947493650609e-8 (weight) ^2 + 0.022876125494594512 (weight) + -11.049728888935046
cost = 0.000010933293638842444 (weight) ^2 + 1.508941645636664 (weight) + -561.6164658286974
input = -2.9309304319429788e-8 (weight) ^2 + 0.03854067358320092 (weight) + 3.0358900508758735
These are the result of standard 3 point quadratics. The input formula starts to fail (IMHO) for stills over 151,940kg (the point where input in Kg and output in Liters were equal). Beyond that point I ignore the formula and simply set input to the calculated output value. Weights of less than 500kg also produce unuseable values. My thought on this is that stills that weigh less than 500kg are unable to produce 1 Liter per day of pure alcohol, even though they may be able to produce smaller amounts of recreational alochol. Feel free to adjust any values to ones you agree with.