I can't speak to conditions 50 years ago, but I started at a state university 40 years ago, and at that time, it cost about $5000/yr with tuition, fees, books, and cost of living for a year, or $20K for a bachelor's degree. That's about $60K in today's money for the full four year degree including everything. As you say, even a state school costs about four times as much now. Private schools cost $60K+ per year for tuition alone, not to mention the cost of living, which can be super expensive in places like Cambridge, MA or other top university locations. It's not necessary to attend an expensive private school to get a good four year degree, but even a decent state university costs a fortune now.
Edit: when I think about the cost of living back then, I think prices have come up more than 3x since then. $30K was a good household income back then, way better than $90K now. $10/hr was a living wage that could support a family. I'd have to say prices have actually come up 5x since then, so $5000/yr for school is more like $25K now. That's still a lot less than I think most students can work out now. In some less expensive states, where the state university is located in a college town that doesn't have big city living expenses, it may be possible to get by for $40-45K per year including living costs. In a lot of coastal states, I think higher living costs for a single college student in the dorms or sharing an apartment with roommates would still cost at least $60K/yr altogether.