You're absolutely right, I was far too generous. For a sensible size of production run, your $6 figure is much closer to the mark. I made some faulty assumptions about the amortized cost of tooling for the plastics and over-estimated the cost of both the OLED module and the li-po.

In my (pointless and lousy) defence, I'd say that I'm used to making extremely conservative estimates, because nobody ever got fired for coming in early or under budget.