Each school/program sets it's own tuition, so the amount unfunded grad students will be billed will vary from school to school. I assume the process is similar to that of financing undergrad. You'll have "pending aid," be billed for a semester, then when your loans come through, the school will be paid first, and any remaining funds will be disbursed to your account.
Bestcolleges.com says
"How Much Is an MFA in Creative Writing? According to Peterson's, a higher education organization, graduate students who attend a public university pay $30,000 in average annual tuition, while those who attend private institutions pay $40,000 each year. However, prices vary with individual schools."