There's a world of difference between a hobby project and a large-scale production item. The CPU in the smart meter likely isn't much more powerful than an ATTiny. By the time you've scaled this project up to meet the needs of the electric company, the cost is likely comparable to what they already have.

BOM (Bill Of Materials) cost is rarely the limiting factor on commercial products. The selling price of most devices is usually a large multiple of the cost of components.