David,

St. John's, Newfoundland (CYYT) LOC(BC) 34 has an MDA of 255 ft.
There are a few other non-precision ones with less than 300 ft. in the
Maritimes, mostly because the approach is over water, I suppose.
The highest approach I know of is Faimont Hot Springs, B.C. (CYCZ) NDB
A with an MDA of 6322 ft.

Gerd
T182 C-FDOW