You might check around for hardwood suppliers in your area. I’m fortunate to have a couple of local mills within 15-45 minutes of my house and another within two hour drive on a route that I frequent several times a year. I can sometimes source local, dried hardwood at prices competitive with construction grade lumber. I don’t think there is any shame in using construction grade lumber. For some, their first bench is their last bench. For others, they may build multiple benches for their shop. My first bench served as a stationary out-feed table for my craftsman tables. It was built with construction grade 2x4 posts, 2x6 stretchers and a repurposed laminate covered desk top. I threw on a used 7” Wilton quick release face Vice. This bench is ugly, but it is solid, and serves a purpose. If you build the AA bench, I am sure you will be pleased with the result regardless of wood species. As noted, in your shop environment, you can expect some movement. If after the first bench, you find yourself loving the craft, but unhappy with your shop, that may motivate some rehabbing of your space to make it less susceptible to the climate. Be sure to share your progress. Have fun with the build.