So the logical question becomes, how many 3-d printed guns would you have to turn in to amortize the cost of the 3-d printer?
It depends on what is offered, but on the order of 1-5.
A suitable starter 3D printer can be had for about $250.
The big cost is not the printer or the filament. It is the learning curve to use the printer.
Well. . .you can buy an Ender3 for around $200, and a kilogram spool of PLA for 20-25 bucks each.
A minima! 3d printed pistol takes about 500 grams of plastic.
So it would depend on the buyback offer, but likely anything over 50 bucks would be pure profit for over 6 or so pistols...