Of course this cost would be distributed over time, and the economic benefits of putting substantial spending money in the pockets of younger adults would have the potential to significantly offset or exceed these costs.
Trump-led tax cut policies reduced revenues by ~$1.5 trillion in his first term, and ~$5 trillion in his second term. $800B of PPP loans were forgiven. The oft-cited ICE and CBP budget increases were about $140 billion.
I can't find many other policies championed by Trump that accounted for increases >$200B in increased spending. As a result, there's not really any good 1:1 "Trump is willing to spend $400B on $X but not student loans". Most of his national debt impact has been via tax cuts rather than spending. Where spending did increase in large amounts, it was mostly for the Pentagon, and some % of those increases likely would have occurred under any other administration - so it's hard for me to carve out what Pentagon budget increases were due to his policies vs. the base-case for how much they would have increased otherwise.
I think the best course is to allow students to default on their loans. With backed loans Unis know they’ll get their money one way or the other and keep ballooning their admin costs.
We can do both. We can help people already saddled with debt, and also do things to prevent future generations from being saddled with debt in the first place. People who managed to climb out of the hole (a demographic I am also part of) are the least in need of consideration.
But more generally we shouldn’t do one off things like this when we still haven’t fixed the cause of the problem. A better policy would be to start by making community college or first two years of college free or something like that.