> The 500D I'm finding is ~$15/yd before shipping...
That's pretty good. You won't need much fabric for one pair, so 1 yd will last for several MYOG pairs - MANY years. very cost effective.
Actually, for some very strange reason, the gaiters I make myself using 500 denier Cordura seems to outlast commercial gaiters by a factor of 3 - 5 or more. That's leaves me to wonder what is the rubbish some of them are made out of?
I don't like the idea of a detachable upper myself, fwiiw.
I have recently switched from 20 mm Velcro tape at the back to a #10 zipper, with a large snap at the bottom. Seems to last better than the Velcro.