While there's certainly mark-ups, the most popular modules are made by their manufacturers rather than outsourced to China. Doepfer in Germany, Make Noise in the US, Intellijel in Canada, ALM in the UK, Mutable Instruments is outsourced but only to another part of France. Long lead times on certain modules are par for the course when they're being made by one person. Of course, when it's one person making everything, the total output of stock is going to be low, and thus the economy of scale that something like a Raspberry Pi is able to take advantage of is reduced, especially with moving parts like potentiometers, which can cost more per unit than a micro-controller.

There are people making modules for dirt cheap with razor thin margins, mostly as a side job, and there's always the DIY route if you want to save a few pennies.