When travelling around Nepal one of my mates commented that he could not understand why there were so many small motorbikes around when he would not consider buying anything smaller than a 250cc.
At the same time he was aware that our porters were very happy to get a job at $2 US a day... (10 of us employed 23 locals for the 3 weeks)
And that is the problem that so many "easy" projects are just not affordable in many countries.
Here is another article that gives a bit more of an insight on what is all about :
http://www.core77.com/blog/sustainable_design/the_biolite_stove_19707.asp
Can't find it now but the founder also did mention something about the relationship between numbers and costs , basically the more you make the less the cost per unit.
The aim was for $20 per unit , that is for the "home" type.
Franco