Denmark spends about 0.7% of GDP on the "SU" student support system [1]. The same proportion of American GDP would be $110 billion; $24 billion would be a mere 0.15% of GDP. So I don't think there's a feasibility issue; it's clearly possible to spend as much as 0.7% of GDP on such a scheme. The U.S. has many more students, but also a much larger economy. I agree that such a scheme would be politically difficult to pass in the United States, though. I suspect the U.S. will end up spending a pretty large amount of money anyway, but on a more haphazard scheme rather than direct grants, such as occasional student-loan amnesties, or more heavily subsidized loan interest rates.

[1] Somewhat outdated figures, but I believe still roughly accurate: http://www.sustyrelsen.dk/udst/in_english/cost_of_study/kap4...