Thanks. What would an OEM's markup be selling to a 'manufacturer'?
Good question. In my experience, the OEM would be charging the manufacturer ~80units.
This can be a bit tricky though, and you could break this stage down to another 3 or 4 layers. Let's say a camera has an image sensor, a DSP, 500 resistors, 500 capacitors, Ethernet/PoE magnetics, and other components. In some cases the OEM will sell all of that stuff to the "manufacturer" in the form of the finished good. In other cases the manufacturer actually sources all those resistors and capacitors and whatnot from electronics distributors (Digikey, et al) and sends them to the OEM for assembly into the finished good. So that 100unit BOM might be 50units to the OEM, 40units to Digikey, 10units to Ambarella (or whatever). Some of that can change based on volumes. Digikey has their own markups, but at some point you might buy direct from some of the component manufacturers themselves.
Cases are another variable scneario. Sometimes you can modify an existing case to customize it for your needs. But more commonly, you have a tool/mold made for your own injection-molded stuff. That can be 20,000-50,000 "units", so the more finished cameras you sell, the more that cost is spread across things. There is also stuff like UL testing and so forth that the manufacturer bears.
What a lot of this adds up to, is that the manufacturer may have the biggest margin by far, but they have a lot more up front costs vs. the other players. I realize that EVERY business has overhead (office/warehouse space, etc.), which the manufacturer ALSO has on top of the other costs.
Is the distributor usually an optional channel partner or obligatory one?
Distributor is totally optional. However, if you don't use a distributor, you're probably paying a 3PL firm to store and ship product, or you're paying extra people to run your own warehouse. Not to mention the credit aspect. The distributor is going to pay you pretty you pretty regularly in 45 days, but the average integrator wants to pay 90+ days out on average if you don't have some extra AR people to stay on top of things.
The thing to keep in mind with distributors is that they are basically a trade-off for internal costs. You can pay a few points to a distributor to be your warehouse and credit department, or you can do that in-house. Distributors like to market themselves as a way to increase your sales, but this is becoming increasingly less common, unless you pay additional marketing fees to get highlight placement in catalogs and email blasts. There is also the somewhat harder to measure cost of having product at too many distributors, as you'll typically want to have inventory at all of them. So, if you have 5 distributors, each with 200 Widgets on hand, that's 1000 Widgets you have spread around. If a dealer wants to order 250 Widgets at once, now you're having to pull inventory from one to send to another and so forth. Not to get too far off topic, but this is one of the reasons manufacturers will offer product registration discounts, they want to know about big projects coming down the pipe, who is going to win the deal, and where they are going to buy from to make sure the inventory is ready when the order comes in.