I assumed we were talking about someone buying gears from a 3D printing service. Then the cost increase for metal SLS seems negligible compared to the increase

I assumed we were talking about someone buying gears from a 3D printing service. Then the cost increase for metal SLS seems negligible compared to the increase in robustness. If you're considering forking out $10K for a printer, OTOH, it means that you'll be running it for larger production runs, and then you might as well just get some molds made for traditional powder metal sintering. Especially when you factor in labour costs.