If you sell me a 2" by 4" board, you cut it 2"+the width of the sawblade, just like the metric boards are sold.

Also is a saw really 1/2" wide? That’s like 1.27cm, that’s wild.

If you really really cannot sell a true 2"x4" at the price of a 1.5" x3.5", just keep the same price and call it what it is.