Not true. The price of materials and the energy needed to run it determines the lower limit on cost for AI. The cost of energy to run computers is pretty low -- low enough that a lot of people don't really think about it until you get up to clusters of the size found in computer labs and data centers -- but it's not nothing either.

I will agree though that the minimum cost to run a super-human AI (once it becomes available) is likely to be substantially less than the minimum wage needed to pay humans to do equivalent work.