I've been 3D printing as a hobby for a couple of years now, and have always heard how 3D printing is great for prototyping, but once you get beyond 10 or 20 pieces it's just not cost competitive with other technologies. I just accepted this to be truth, and have even told some of the customers I've gotten through 3DHubs and other marketplaces the same thing.
Now I'm creating an item for resale and am 3D printing the case. As I'll need 40 - 50 cases at a time I thought I would shop around for other options. But I just received some quotes back on injection molding. The mold price (for half the case) was \$15k, plus \$10 per unit at a quantity of 50 and \$4 per unit at a quantity of 500. Even in the case of the latter, the cost of tooling plus production is \$34/piece. 3D printing the same part myself costs $7 in filament, and paying someone else to 3D print it cost \$28.
Keeping in mind that 3D printing allows me to make changes to the design on the fly and print the exact number I need without having to worry about volume discounts, I now wonder if I've just been repeating a common misconception. Is 3D printing really noncompetitive for medium (10-500 pieces) production runs? If so, what makes it noncompetitive, given the extremely high up-front cost of IM?