When you upload a file, the price appears in about a second and people reasonably wonder where it came from. It is not a lookup. It is four numbers added together.
- Material — the actual volume of plastic your model uses, shell plus infill, plus any support the shape needs.
- Machine time — how many hours the printer is occupied, which scales with volume, height and layer height.
- Complexity — a small surcharge for models that are dense or heavily overhanging, because they need more watching and fail more often.
- Setup and handling — a flat component covering the file check, the plate, packing and shipping.
Why small objects look expensive
Below a certain size, the flat part dominates. A tiny keyring uses almost no plastic and almost no time, so its price is essentially the setup — which is why the number stops moving when you change the infill on something very small. That is the minimum charge doing its job, not a bug.
Why quantity helps so much
Ten copies of a part share one file check, one plate setup and one package. The per-unit price falls accordingly, and keeps falling up to about fifty.