Last time I looked into this, there were under 20 million college students in the US, and average in-state tuition was around $5,000. What the heck, let’s call it $10,000 to be safe. 20M x $10k = $200 billion. That’s what our first year in Iraq cost us. So, yeah, free college education is feasible if we as a nation decide we want to invest in our human capital instead of squandering our resources on elective wars or tax cuts for the rich. (You can get the latest figures on enrollment and average tuition from the US Census.)
But the question asks what I personally would be willing to sacrifice for this goal. For the sake of simplicity, I’ll say that I would be willing to pay at least another $1000/ year to fund universal post-secondary education, provided that the tax increase were progressive (i.e., people who make a lot more than me would pay proportionately more than $1000) and appropriate strings were attached concerning how those funds could be used (no rip-off for-profit “universities”, no scammers dropping classes as soon as their aid check clears, etc.).
Concerning the value of philosophy, history, etc.: the framers of our constitution did not invent the idea of a republic or a union of states. They were all well-versed in the writings of Aristotle, Cicero, Machiavelli, Locke, Hume, and Montesquieu, and in the histories of republics and confederations of states from ancient Greece onwards. They were able to apply those lessons successfully and improve upon earlier models. Moreover, they understood that a popular government cannot work if the citizens could not think through the issues and were easily swayed by the specious arguments of demagogues. The liberal arts—when taught correctly and studied diligently—improve students’ ability to reason cogently and communicate effectively. If college education is to be free, more study of philosophy and history should be required, not less. If the public is paying for it, then a college degree should help prepare students for their roles as citizens, not just workers.