OLPC talk:Community Portal
May I suggest (again) that models distinctly different externally (in color/shape of case, with a different logo, say) be made and sold on the market for a 50% premium ... with the proceeds used to build and distribute the OLPCs. I think you might be able to pay for much of or the whole thing that way ... PLUS the larger market would bring the price per unit down anyway.
The distinction needs, of course, to be virtually inimitable in the practical sense, like case shape and logo (and of course protected in every country re copyright).
One bonus is that everyone who owns one of the latter can clearly be seen to have contributed to building the OLPCs, hence a bit of "pride of ownership". A sort of a more expensive "yellow wrist band" idea ... and more useful.
Good luck with the project!