Structural reinforcement is unnecessary - they can be stacked half a dozen high safely. A bit of back of the envelope tells me the cost of paint to coat the exterior of a standard 2 story suburban house is about $1500, so I estimate painting a 40 foot container should be about $400 max. Insulation should be about $1K. I imagine for drainage a buried septic tank is the best solution here.

I think the cost to retrofit an otherwise sound but unwanted container is less than the cost to purchase a used one. That is orders of magnitude lower than the cost to erect "standard" solutions to the housing problem.