I said pretty clearly:
"As long as an industry is growing - there will be money to invest in lowering costs."
Once everyone is drinking milk, there isn't much room to dump money into lowering costs, because the profit gets squeeze out of the industry from competition. Many things do hit a floor and level out in price. But there is no reason to believe solar is anywhere near that floor. The raw material - silicon - is one of the cheapest and most abundant materials on the planet. Those lower cost rules don't go on forever for all products, but they are valid for periods of development in a product's life cycle. And I believe solar power will be one of the most important products of this century, so there is lots of room for growth. Humans cannot afford to keep hurting the Earth to get our energy, and solar presents a clear opportunity to harvest thousands of times more energy than we currently use. The technology is already on par with the cost of fossil fuels and we will continue to find ways to make it cheaper and more efficient.
Also, Milk is cheaper. You just can't tell because our dollars aren't worth the same amount. According to a short search, in 1950 a gallon of milk was $0.80, which is $7.88 in today's money. Milk is cheaper because we have enormous milk factories now, not little farms that have to support a bunch of workers.
And OF COURSE you can't reduce the cost of something below the cost of raw materials, but as I said in my previous post you CAN reduce the cost of raw materials by investing in better mining equipment.