I agree with both Kristian and Tim. All apps and code released under GPL should be free, not only so users in lower income countries can afford Moodle, but simply because distribution of core code needs to be free.
On the other hand, development of code needs to support the coders, so we need an economic model to support them. And people who need particular code, should have a way to show their support and get what they need. So instead of only general donations to the Moodle community, I would also recommend a targeted system which allows designated donations to particular applications, modules or feature enhancements.
That way, Kristian can give her/his one pound to the Mobile Moodle app, and help that corner of the Moodle universe grow and flourish.