The $3 part is only the controller, though. It doesn't actually handle the power itself - it requires extra components for that. It'd be like saying a $100 micr

The $3 part is only the controller, though. It doesn't actually handle the power itself - it requires extra components for that. It'd be like saying a $100 microwave is expensive because it is controlled by a $0.50 controller chip. The project page itself states that the inverter will cost at least $20 in total - and that's using essentially the cheapest components you can find. Once you use quality components and include things like proper input/output protection, connectors, and a casing, you're likely looking at a $40-50 BOM. A $150-$200 retail price is very fair, considering all the other stuff you need to pay for to actually design, certify, make, and sell a product.