The price of everything is going up. It's called inflation. The U.S. government is giving away and/or spending trillions of dollars it does not have. I don't see any difference between what it does and what forgers do: print money that isn't backed up by anything. Add to that the recent increase in fuel prices and our renewed dependence on foreign oil (after we had become independent from it during the previous administration) and you'll figure out that the price of lumber, that requires energy to be harvested and transformed from trees into beams, boards, sheets, etc. and then transported from the mills to the dealers and to the retailers (and lumber weighs a lot, and requires a lot of fuel to be transported) and you'll figure out that the price of lumber will continue to go up. Also, as new federal policies are adopted, many forests that could have used some thinning out will be off-limits to any harvesting of trees, and this will reduce the supply while the demand increases.
When I built two of the three chicken houses I have, I was told by a friend that there was a lumber mill that gave away the outer surfaces of various types of trees that were being sawn off the logs to square them. These discarded boards, flat on one side and round on the other side still covered with bark were piled up on a lawn outside the mill and available to whoever wanted them. With the same friend. we went to that mill and found out where the cypress board were. We cut them in pieces that would be manageable, piled them up in the back of my F 150 and made several trips from the mil to my home. The only plywood sheets I had to buy were for the roof of the chicken houses, and then the roof was covered with more of those boards. The sides were built with the cypress boards, with the bark on the outside, overlapping like roof tiles, so that the rain wound not penetrate. I live in Alabama, so airtight chicken houses are not a necessity. On the contrary, air flow from the gaps between the boards is essential in summer, and those two houses are many degrees cooler than the outside temperature. In winter it never gets really cold, but if it rarely does get below freezing turn on heat lamps in these houses.
Cypress wood does not rot, and if you could find a friendly lumbermill owner that gives away or sells at low price these discarded outer boards (non suitable for much, because if you burn them they release toxic fumes) you'll be able to build chicken houses for much less than by buying treated plywood. As an added bonus, my two chicken houses look like log homes, of the rough kind that were built by gold miners in the Yukon. Incidentally, those boards can make excellent deer blinds, too, as they seem to repel insects and larvae. If I were to build deer and turkey blinds with them, I would follow a different pattern and fit the boards together vertically, rather than horizontally, so that the blinds would look more natural--like the trees that surround it.