Well, maybe there should be a 1-month “introductory price” for ~$30-40, after which the price drops to ~$20, and everyone who orders at the “introductory price” will be helping to pave the way for the next set(s), and then when the sets are finally finished, the folk who paid the “introductory price” can get the last set or 2 for free.
Another thought would be, that since several people want to help get this project moving right along, so maybe you could price individual sets for ~$19.99, but go ahead and let people order “complete sets” but paying money up front (like ~$50 for the first 3 country sets or ~$100 for the “complete” 6-country set. Then when the sets are released, then just ship them right out to the folks who already paid for them.
Just a couple of thooughts.