Less than $40 out of pocket. The cab was given to me for free, and I had most of the parts on hand. Biggest expenses were a new light bulb and black mat board for the monitor bezel.
The whole idea of cheapest build is different for everyone I guess.
If you already have a computer on hand, tools, and a monitor. I wonder how those should count towards the cost. My first cabinet was super expensive because I had to buy everything to build a cabinet. Cabinets 2,3,4, and 5 became cheaper as I was able to use parts from the previous build.