With good collaboration tools, for many kinds of tasks testing the commitment of volunteers by putting them to work should be rather cheap to test, especially if they can be given less time-critical tasks, or tasks where they help speed up someone else's work.

Serious thought should go into looking for ways unpaid volunteers could help, since there's loads of bright people with more time and enthusiasm than money, and for whom it is much easier to put in a few hours a week than to donate equivalent money towards paid contributors' work