I thought 3D printing was expensive, I wonder what the profit was
Depends upon the machine and what the printing feedstock is.
You can get a "thermal melt" machine for around $150. The standard PLA feedstock is about $75 a reel.
Ellegoo or AnyCubic resin printers run about $300-400 for the smaller ones, the resin is all over the place for price (very much linked to final product strength and whether isopropyl or water washed). Much like reloading, you wind up wanting a machine for rinsing finished parts, and another for UV curing the washed parts.
But, once you have bought the equipment, it's really down to how a person calculates their own man-hour pricetag, and the cost of the materials.
Now, if you send out parts for others to print--that's pretty steep. But, they are paying for operator labor, overhead, and all the rest.
If you are "scamming" a buy-back, you need not use your expensive, load-bearing feedstock--your "expense" is the hours of run time and the feedstock cost (which can be a "sunk" cost, if you are no longer using a given material for test shots, for instance).
To use a reloading example, how much "cost" is there if you just seat cast "junk lead" bullets in un-sized, un-primed, wore-out cases?