I have a 99 year-old Craftsman bungalow in Portland Oregon. The steps to the front porch are painted 2 x 12s, which is what most of the houses in the neighborhood use. The paint takes a beating with our wet winters, and the steps need to be re-painted every year. Now I'm starting to get some peeling of old paint layers (I'd like to place the blame for insufficient prep on the previous owner ;-), and the steps are looking pretty ratty.

I'd like to replace the current 2 x 12s with something that needs less maintenance. I don't mind staining every year, but I want to get away from sanding and painting every year.

So...here's the deal. The house siding goes around the sides of the staircase, and I'm not sure I can remove the existing stringers without taking off the siding. (This photo is not my house, but it should give you the idea:

I want to do this quick and easy, so removing and then replacing the siding to get at the stringers is out. If I keep the same stringers, I believe I have to use 2 x material to replace the stairs (that is, if I use 1 x, it will screw up the stair dimensions at the top step).

That's is too bad, because I'd really like to use ipe or cumaru 1 x 6s, or maybe 5/4 x 6s, because I can get those locally. If I get 2 x 6s in either material, I would have to get it shipped, and from a strength perspective, it seems like 2 x 6 stairs would be way overbuilt. Am I right that replacing a 2 x plank with a 1 x or 5/4 x plank will make the stairs hazardous to use?

Taking all the above into account, my options seem to be, in rough order of cost:
-2 x 6 ipe (don't see 2 x 12s anywhere, and they would be out of budget anyway)
-2 x 6 cumaru (again, don't see 2 x 12s)
-cedar in either 2 x 12 or 2 x 6
-redwood in either 2 x 12 or 2 x 6
-fir in either 2 x 12 or 2 x 6 (Salvaged old-growth fir is easier to find around here than a hoppy IPA)
-pressure treated pine in either 2 x 12 or 2 x 6

Any suggestions? Is it possible to get away with 1 x 6s? If not, which material would you suggest, and why? I'd like to spend less than $500 on the materials if possible, but 2 x 6s of the tropical hardwoods would likely cost more than that, especially when considering shipping.

Thanks!