Shop local. Big box hardware stores are NOT the place to buy lumber for projects like this. If you need a stack of kiln dried 2x4s, sure. If you're timber framing or making yourself a work bench, you can save money and get better lumber by shopping at a local sawmill. Yellow pine is a dollar a board foot for us. Some places it's a little more. Some places it's even less. That's why the long form video calls it $50 to account for a little extra cost, nails, and tax. Do the math. 4x4x120 = 1920. 1

How to Calculate Board Feet Lumber and Cost | Material Estimator