It says the cost of the project needs to drop by half not the cost of the batteries. It could be that the cost of batteries is only a small amount of the overall cost. That is what you see with solar, most of the cost comes from installation.
Manufacture larger self-contained units the size of a standard shipping container?
IE: http://www.powertechsystems.eu/home/tech-corner/lithium-ion-...
Not sure how that carries over to larger batteries as I've only really dealt with them for ATV type use.