I don't doubt the price will drop as they become more popular (it's probably a few dollars worth of raw hardware), but right now it's a fairly niche product.

"a campaign where the cost per unit goes down as they reach certain sales goals."

That's an interesting idea. It gives purchasers an incentive to promote the campaign, as opposed to "early bird" specials which incentivises early purchasers, but almost disincentivises later purchasers.

This has been done on Kickstarter and software bundles like MacHeist in the form of "unlocking" additional rewards, but I don't think I've ever seen them actually lower the price if they hit certain goals.