have they tried the lottery grants? The problem is that i would imagine that if it's "just" a nursery (as opposed to, for example, a special needs nursey that is not provided, but needed in the local area) then why would anyone want to donate? After all, its only going to benefit a small exclusive group of children that go there, and if it's a fee paying nursery, then its only benefitting the children of affluent, middle class families (even more of a no-no in today's p.c. world)
sorry if ive read the situation wrong, but you would be in a better position if you had an issue to hang the appeal on, rather than just the owners were greedy and wanted to sell out for the cash!