I am not familiar with an LAA permit. In Canada, a "permit" aircraft is very likely not a type certified model, and thus not eligible to be modified in accordance with an STC. I can issue a Canadian STC only to a type certified aircraft, with a C of A. Mogas STC's require a lot of testing, and are disproportionately expensive, relative to the type of aircraft, and operation. Those who have achieved STC approval of Mogas have make expensive investments, and that's why the STC's have a noticable cost.