With hand-built cartridges that are built by one person (as is the case with us, and I assume Shelter), the builder works most efficiently when he is building a single type of cartridge, in continuous production-line fashion.
Having different models in the lineup detracts from the builder's work efficiency, and results in less production capacity. But since a cartridge brand needs a variety of models, the normal practice is for the builder to work on reasonably-sized batches of cartridges all of the same type, with different cartridge models being made in individual production batches.
Usually a cartridge builder won't want to work on different cartridge models at the same time, as each model will require different parts, different tools and different procedures, which slows the overall building down and increases the likelihood of errors, and some of those errors can be expensive. For example, if the builder mistakingly puts stereo coils into a body that has already been silkcreened as "Mono" and solders the connections in, at the very least the cantilever and coil assembly will have to be thown away.
For cartridge models that are in high demand, having multiple cartridge models isn't so much of a problem, as each batch of cartridges can be large enough to keep the builder's efficiency high. But with cartridge models that are in much lower demand (as is the case with mono cartridges), the batches wil be small enough to not lend themselves to efficient building.
Also, the parts for a mono cartridge are different from a stereo version, and will be ordered in much smaller quantities (in consideration of the lower demand). The cartridge builder has to pay more for small-quantity items (and may have to wait longer for them to arrive), and mono cartridge parts definitely fall into this category.
All of the above means that for a cartridge builder, having mono cartridges in the product lineup is counterproductive for efficiency of time and cost spent, and therefore business. That's why a mono cartridge will be sold for more than its stereo equivalent (as would be the case with any semi-customized, low-demand model). The difference in pricing surcharges that various cartridge manufacturers list for their mono cartridges as opposed to the stereo equivalents will be tied to how negatively they each evaluate the reduced efficiency in time and cost.
Cheaper cartridges like the Denons aren't hand-made (AFAIK) and likely are made and sold in greater volume, and therefore the above may not apply.
cheers, jonathan carr
