The issue is no one cares what something cost to build or the time it takes. They just look at the value of that item to them. Being very honest,, looking at it, my question would be why waste the space on something as big as a machine when I could just put the boards into a machine to test them?
I had a nice set of the "original" Bally testers and sold them because of the wasted space. Pinitech makes little portable testers that help locate most issues and they will fit in a box the size of a shoe box. Why have something this big in limited space.
As far as DIY tool that helps you - great - but as far as building it to sell I doubt there would be interest at any price just because space is a huge issue for most people in the hobby.