Head for ze hills. Considering only one or two companies actually manufacture consumer-grade 128GB microSD cards, and that they always go for ~$100; if they were available much cheaper (such as $18 to $38), a bunch of companies like Kingston or PNY would be releasing them at that price. That they aren't even out there precludes production costs are viewed to be too high vs. demand, which is why SanDisk version of the 128GB microSD is the only one usually found at retailers.
I wouldn't risk it.