when a dive shop sells a course (through PADI, SSI, or NAUI, to keep it simple), how much of the total cost goes to the dive shop and how much goes to the certification agency? Is it different for the OW certifications vs. speciality courses?
The simple answer is that the majority of what a student pays for a course goes to the dive shop, not the agency.
Jim provided a very good response. The agency generates revenue from affiliation fees (shop AND instructor, for that matter), they generate revenue from the educational materials (manuals, DVDs, etc) sold to shops which are then resold to customers, they generate revenues from the sale of (required) instructor materials, they generate revenue from the processing of certifications. (And, they now generate revenue from selling eLearning directly to consumers.)
The fees charged for courses by a particular shop reflect that shop's business practices, and there isn't an agency percentage 'cut', per se. We
do pay the agency (PADI in our case) for the certification PICs - either the paper version or an online processing unit - that we use. We buy those in bulk, and use the same PIC envelopes (or online processing unit) for OW, AOW, Enriched Air, Tec, etc., etc. So, the agency cost per student is the same across courses (whether OW certifications or specialty courses), irrespective of the shop fee for the course. And, to answer part of your question, that amount is relatively small. We add that fixed cost per student into the calculation of the fee we charge for the course. We set the course price according to the level of effort involved (including instructor compensation), AND the market. The agency has nothing to do with what we charge. If we wanted to charge $950 per student for a group OW course we could, But, we don't because the market won't support that, given the competing prices from other shops (with the same, or other, agency affiliations).
Our approach to eLearning may be a bit different from that used by other posters. We charge less for an eLearning course compared to a 'traditional' course, although the differential varies across courses. For example, for the OW course, we adjust our fee so that the total amount the student pays for an eLearning OW course - the fee they pay to our shop combined with the fee they pay PADI for the eLearning - is the same as what they would pay the shop for a traditional OW course. Our price structure reflects both the intensity of competition at the OW level, and a desire to promote eLearning at the OW level. For AOW, as a contrasting example, the differential between the 'regular' course fee and the eLearning course fee is much lower than the cost (to the student) of the eLearning. A student who wants to do an eLearning AOW course with us will pay quite a bit more when the combined cost of our fee and the PADI eLearning fee is considered. So, we offer the option but don't encourage it.