IME big box store prices are 2-3x that of a real lumberyard for low volumes. I don't think they're reflective of the rest of the market, especially at high volumes. When you're talking an order of 100 or 1000+ board feet from a lumberyard, it's a completely different story. I've had situations where the last mile delivery fee alone was 25% of the cost, not including the cost to get it to the lumberyard in the first place.