I had the brainstorm to check into Al EMT when the price of steel started going up.
I've not seen it in sizes smaller than 2-1/2", (but that doesn't mean it doesn't exist, of course).
I found that the price of aluminum had gone up just like that of steel, and the only appreciable savings would be that of installation. 1 man can easily install 4" alone [Linked Image]

I love the stuff, just be sure to use lots of lube.