I looked this up just the other day because I made myself a new deep box with finger joints. The wood cost $15.00 at home depot and would make 1.25 boxes. Western Bee sells the unassembled box for less than $9.00 or $11.25 for 1.25 boxes.
If I had a lumber mill close by I would look into mill ends or ask about lumber cut closer to the dimension I need. I would not want them pre cut to width but closer so that there is not so much waste. you can figure almost a quarter of a 1X12 is waste. In this case that is $3.25 of wood that went on the shop floor. I can use two small pieces of it for hand holds and that is about it. even with adjusting for what I really used I built a box with $10.00 worth of wood that I could have bought for $9.00. Cheaper wood is a must if you want to save money making boxes. Very cheap wood.