We all know a college education is expensive. But that's not the worst news. The real kicker is that a diploma has become significantly less affordable over the past year.

According to a new study, "College Affordability in Jeopardy," tuition at public institutions is rising, while financial aid is shrinking.

"The states are responding to the budget crisis by passing major cuts on to colleges and universities -- and colleges and universities are responding to these reductions by passing on the cost to students and families," said Patrick M. Callan, president of the National Center for Public Policy and Higher Education, which conducted the study. "This is all happening at a time when student financial aid is not keeping pace with increases in tuition."

According to the study, states have increased tuition by as much as 24%. Earlier this year, the College Board announced that tuition at four-year public schools rose an average 9.6%. Meanwhile, state support for higher education grew just 1%, on average, nationally.

America has a noble yet flawed idea about a college education: A diploma is worth whatever price is paid.

Sure, plenty of studies find a college graduate will earn almost twice as much as a high school grad over the long haul. However, as growth in tuition has outpaced overall inflation and personal income, more and more students are graduating with crushing student-loan debt.

Something will have to give. Will only middle- to upper-income families be able to afford college? Will schools cut funding for extracurriculars, such as sports programs that don't pay for themselves? Will people still want to pay thousands of dollars for a class on Philosophy and Star Trek?

Before that future plays out, do what you can to keep your own college costs down. Start saving as soon as possible, and look for schools that will provide the most brain for the buck.

To learn more, visit our College Savings Center, or check out our latest book, The Motley Fool's Guide to Paying for School: How to Cover Education Costs from K to Ph.D.