With a Mick Strider custom (and pretty much any other custom knife, for that matter), the main thing that you're paying for -- in other words, the thing that's primarily responsible for the difference in cost between the custom knife and a production knife with similar materials -- is the labor of the knifemaker. The more skilled and well-known a maker is, the more his time is worth/the more he can charge for his services. Obviously, this isn't unique to knifemaking. The same principles apply in any domain where skill and reputation are major determinants of prices, whether it's buying/commissioning a work of art, hiring a band/photographer for an event, picking an architect to design your house, and so forth.
(Also, a different grind may seem like it's only a minor difference, but it's something that takes hours of labor -- especially for something as complex and unique as Mick's nightmare grind!)