We recently posted a wiki page summarizing XO prices (roughly $185-$205 by quantity), and how to get XOs for your own deployment: Buying XOs. The minimum order is 1,000, with occasional exceptions made for orders as small as 100.
In addition to our national partnerships, OLPC regularly sells XOs to groups all over the world who are running pilot programs in their district or community. While we do not often sell in quantities of less than a thousand laptops, exceptions are made for programs that have planned for a successful deployment. (And we feature some of the best-planned grassroots programs here on our blog!)
For groups working in war-torn or post-conflict regions, we may also be in discussions with aid groups who could help support a program. Feel free to get in touch with us if you are planning a sizeable project in these regions. For more information or to place an order, email us at firstname.lastname@example.org.