Probably the best thing I learned about Elon Musk in the Walter Isaacson biography with this notion of the “idiot index; the general idea is simple: consider the raw materials minus the markup.

The lesson then is simple:

The price you should pay should always be closest to the raw cost of materials.

Example, if you go on Alibaba, you could literally print a cotton T-shirt for one dollar!

Things with a high idiot index include iPhone pro, etc.