My guess on why it costs so much / why Unicomp can't do it, judging by
this.Dye sub involves pressing a dye sheet against the caps at high heat. In order to apply pressure, you need a press or some sort of tooling that fits the keycaps snugly.
That piece of tooling is why dye sub costs so much/Unicomp can't do it. Presumably, SP needs to tool the press in order to do dye sub, which jacks up prices, and Unicomp's tooling is specific to the shape of their keycaps, which is why they can't do Cherry caps.
Also, if this ever goes through, do multi colored caps! Take advantage of that, or else there isn't too much of a point over double shot.