Furu I saw that post of yours (very nice) when searching about the siding jig. We have a large local pine mill that will sell directly to locals (they are 100% exporters and trailer loads only), I can buy 1x shiplap planed 1 side for under $450/1000bd/ft. That is an "industrial" grade with knots but kinda hard to beat.
I use it for sheds and a camp buildings, I like the added strength (thickness), but I do have to put blocking in the walls, I can't see running it horizontally.