A while back I ran several test with 3Dhubs and found the the best way to stay (mostly) competitive was to charge $15/hr for my machine time with a 5 hour minimum. (Their curve didn’t appear to be linear, but more exponential with the curve starting off steep and then flattening out as you approached larger and larger jobs). I liked this hourly rate because its easy to quantify in QuickBooks, and if a customer needed finer resolution, the extra time appropriately added extra cost (even through the resin I used didn’t change)
However, with every software update, the estimated time in preform varies like crazy, and it rarely matches the ACTUAL build time, so its not a perfect system
So… how do you calculate YOUR costs to charge your customers? (by volume? Time? other?)