SS is so much better than galv, I just removed some SS screws from a
door sill installed 15 years ago; they look like new.

Isn't your work worth the minor cost increase? Compared to the rest of
the material & your labor the cost of SS is small

McMaster.com has a huge selection of SS fasteners (18-8 or 316, if the
environment is marine).

I use SS fasteners in my 16 gage & 18 gage nailers for any outside work
but you have to buy them is large batches.

cheers
Bob