You can also make a "batch" of holsters in the same manner as you would a production run of holsters. Even if they are different patterns for different weapons, you can cut out a batch of say 20, of whatever you have orders for or want to stock. Then assemble them all with a pretty specific list of steps which are common to most pieces. For example, cut, glue, sew, mold, dye, etc. This is a lot faster, at least for me, than the one at a time approach, yet each holster can be considered custom. I also think it is a very good idea to have partially completed popular designs put together when time allows.
As to the custom vs. semi-custom vs. production holsters, I think there is a market for all, but they do have to be priced to match each catagory. You will have to decide whether you want to accept market prices for "less custom" pieces.
Sam