Although I am apt to agree with you where the money will come from in general, my thinking is that the value gained from the increased access to this education will offset the costs, -that the ROI makes it worth it. My wish would be that a progressive marginal tax on annual capital gains that began at something like 1M or more would be put to this use, or yes, that we'd stop building so many damned weapons beyond our needs, and that the money could come from there.

As far as evidence, I think it would be hard to come by anything convincing. One might make some sort of hand-waving argument with past GI bills, but there are too many variables in these equations to conclude anything decisively, and your take is largely going to be dependent upon your own politics and value system. My own politics and value system suggests to me that we are spending money in less useful ways, and this would be a good way to repurpose it.

Making someone besides the student pay for community college will not make it cheaper. Increased demand and indirect payment may make it more costly.

In short, I agree with this statement, but believe that the extra cost will be offset by the benefits of a more educated populous.