Please read the information from the Sanders' web site. I think he has been more transparent about how to pay for his programs than the rest of the field.
See https://berniesanders.com/issues/how-bernie-pays-for-his-proposals/

As an example https://berniesanders.com/issues/its-time-to-make-college-tuition-free-and-debt-free/

"The cost of this $75 billion a year plan is fully paid for by imposing a tax of a fraction of a percent on Wall Street speculators " Maybe this isn't detailed enough, but to me it is pretty clear he will impose a micro tax on transactions.

Or for his youth jobs bill "The amendment was modeled on a youth jobs bill Sanders recently introduced to provide $5.5 billion for states and local governments to help find jobs for 1 million young people ages 16 to 24. Closing a loophole that lets billionaires pay a lower tax rate than working-class Americans would have funded the jobs program."