> Stainless steel rebar is a thing. It's expensive […]
That's an understatement. Fiberglass (GFRP) tops out at roughly US$ 2.50/foot, while SS can get up to $9:
* https://www.wellcoindustries.com/the-cost-of-rebar-and-the-c...
The low-end of plain steel rebar is $0.40.
As the GP noted, it's still only a small bump in overall cost.
Also lower TCO, total cost of ownership.