I did a quick analysis of the raw component cost to get this far. These costs are all in Australian Dollars but US Dollars are about the same (currently). The cost, including shipping of components to me and consumables used in prototype manufacture, adds up to about $47. This is less than the prediction of $55 I made year ago, and less than my target of $50. It includes battery, box (with free candy), pcb (from SeeedStudio - if that works out), and all components. The two most expensive components, the RN-42 and MS5611, together cost about $27 base price (about $35 with shipping to me).
Shipping of prototypes from me to Australian customers is about $5, but $10 -$15 to the rest of the world. Each one will take me a few hours to assemble, program and test. I am planning for $70 to be 'unit cost price' to have 10 prototypes shipped to testers. I would love to do it for free but there is no big company to pay.
I think I can reduce component cost by about 30% down to $30 to $35 if I was to make 100, and perhaps down below $25 if I was to make 1000+. But I am going to start with 10 if there is enough tester interest.
Below is a better picture of Prototype 3.