For me, I've calculated that 3D prints cost me about $2/hr to make (on hobbyist level 3D printers), including typical filaments, but not including design time, extra hardware (e.g. threaded inserts, fasteners, etc.), or if I have to remove a ton of supports.
Making quality designs takes a lot of time and money.
- There are many hours spent designing, prototyping, testing, refining designs, etc., then the associated costs of those prototype materials (e.g. printing several iterations).
- You often have to buy items (e.g. mirrors, seals, etc.) so that you can measure them accurately and check fit.
- The cost of discarding or reworking parts that don't meet quality standards.
- Then you have to buy the printer, absorb the learning curve labor of the printer, account for the mainenance/lifespan of the printer, etc.
- If you need Helicoil tools, or other special tools, those often cost hundreds of dollars (e.g. $144 tapping threaded insert installer, $322 Helicoil installer, etc.)
- You need to account for packaging costs (e.g. printer toner to print manuals, cardboard boxes, packing tape, labels, bubble wrap, plastic zipper bags for fasteners, etc.).
So yes, it takes $20 of materials to make that part, but labor, extras, and $1000 (?) of equipment too, so you don't get it for $20. Many may seem silly (e.g. "Who cares about a $0.10 label, a $1 box, or some Windex sprayed on the bed of the printer?"), but I go through hundreds of dollars of this kind of stuff per month.