If donations are that low, have you thought about reducing the hosting package with Invision? That way, rather than going offline altogether, the board may be handicapped a bit, but it would stay online.
You haven't posted the hard numbers in awhile. Maybe if folks knew how close or how far away the totals were from being ok, it would ultimately benefit the board full time by not only keeping things completely transparent, but it would be know how much or how little would be needed to bridge the gap at any given time. Totally list everything, and when all that's needed is a little "push", it could motivate people to bridge the gap as needed. Or, when it's a larger gap, they'll know the size of the task.
I also think it would help folks to know exactly whats going on.