30-40$ is probably a very small apartment. A house (2 levels) in Quebec during winter can go easily around 500$ because of the constant heating required.
Cooling a house during the summer in Texas can easily cost the same amount if not more, and you get a ton of sun during that time. The point is that for single family homes electricity does not usually cost $40/month.
But the price for the equal amount of power walls needed for a bigger house vs a small 1 bedroom raises too, according to the calculator on their site it will cost $30k+ to install it for 4 bedroom house.
