"However, if you go for a mass market, you will need a substantial investment in tooling cost for the enclosure."

This is very true, but not just limited to the enclosure: there is a world of difference between knocking-up the odd one or two units for a specific application, and manufacturing a high-volume Product for the mass market.

For low volume, it's easy to program the odd PROM, tweak the odd pot, configure a few links & switches, hand-wire a few connectors, hand-probe a few test points, photocopy an instruction sheet, stuff it in a cardboard box,...
But for a volume Product, these are all major design issues.