Take one concrete case: a 40 mm square overhang standing 30 mm off the plate, supported at 15% density with no perimeters. That block is 9,376 mm³ of plastic — 11.6 g of PLA — and 25 minutes of printing.
Added to a 100 g part that cost $5.15, the total becomes $5.57. 42 cents — 26 cents of plastic thrown away, and the rest the extra 25 minutes the machine is occupied.
Support density changes it more than you would think
Raise that same block from 15% to 25% density and it becomes 13,920 mm³ and 36 minutes — about half as much again, for material that is going straight into the bin.
Most slicers ship a support density well above what a clean overhang actually needs. Dropping it is the single cheapest tuning change available, and unlike most cost savings it also makes the supports easier to remove.
The costs supports carry that do not show up in a slicer estimate
- Removal time. Hands-on minutes, and on a fiddly part they exceed the print time saved by not reorienting. At any plausible labour rate this is the largest support-related cost on the invoice.
- Surface damage. The supported face comes out rough and often needs sanding or filling, which is more hands-on time and sometimes a scrapped part.
- A higher failure rate. Tall thin supports are the usual thing a nozzle catches on. A support tower that detaches takes the print with it.
The cheapest support is the one you designed out
Tipping a part onto a different face frequently removes every support in it. Chamfering an overhang instead of leaving it square does the same. Splitting a part into two printed flat and glued costs nothing in supports and usually gains strength.
None of those are free — reorientation can cost layer adhesion in the direction of load — but the trade is worth making explicitly rather than accepting whatever the slicer generates.
Size the block in the print time estimator, add its grams and hours to the part in the print cost calculator, and reach for the supports guide when it is the settings rather than the arithmetic you want.