The price ($0.40/W) is the production cost for the PV panel. So, if you want to install, say, a 10kW panel on your roof, the solar panel itself would cost about $4000 to manufacture (as opposed to $8000 by other processes). How much it will cost you, however, still depends on market price, installation and infrastructure cost (batteries, inverters, switches, etc.)
Now, a quick search shows that current panels sell for $250 for a 100W (or $25K for 10kW). And a whole system (< 10kW) is somewhere in the $20-$30K range. What that shows is most of the manufacturing cost of the panels is only a part (30%) of the whole. If all of the saving get forwarded to the consumer, you would see that the the cost might drop about $4K. So basically it'll take 16+ years instead of 20+ years to pay for itself.
After 25 years, you replace the panels and repeat the process, maybe at half the price :)