It's for any income level. Here are some of the terms of some of the programs:
REPAYE program
Your monthly payments will be 10 percent of discretionary income.
Payments are recalculated each year and are based on your updated income and family size.
You must update your income and family size each year, even if they haven’t changed.
If you're married, both your and your spouse’s income or loan debt will be considered, whether taxes are filed jointly or separately (with limited exceptions).
Any outstanding balance on your loan will be forgiven if you haven't repaid your loan in full after 20 years (if all loans were taken out for undergraduate study) or 25 years (if any loans were taken out for graduate...
Income Based
Your monthly payments will be either 10 or 15 percent of discretionary income (depending on when you received your first loans), but never more than you would have paid under the 10-year Standard Repayment Plan.
Payments are recalculated each year and are based on your updated income and family size.
You must update your income and family size each year, even if they haven’t changed.
If you're married, your spouse's income or loan debt will be considered only if you file a joint tax return.
Any outstanding balance on your loan will be forgiven if you haven't repaid your loan in full after 20 years or 25 years, depending on when you received your first loans.
You may have to pay income tax on any amount that is forgiven.
Income Contingent
Your monthly payment will be the lesser of
20 percent of discretionary income, or
the amount you would pay on a repayment plan with a fixed payment over 12 years, adjusted according to your income.
Payments are recalculated each year and are based on your updated income, family size, and the total amount of your Direct Loans.
You must update your income and family size each year, even if they haven’t changed.
If you're married, your spouse's income or loan debt will be considered only if you file a joint tax return or you choose to repay your Direct Loans jointly with your spouse.
Any outstanding balance will be forgiven if you haven't repaid your loan in full after 25 years.
There are other plans. You'd want to read the terms of each carefully. When you apply, you also have the option to tick a box that directs them to assign you to the program with the lowest monthly payment. They would calculate that and do so. You can change programs at any time.
Note that repayments are based on percentages of "discretionary income." The definition of discretionary income is basically they look at the published federal poverty level (for us, overseas, I believe they use the continental US rate, not Hawaii or Alaska) and multiply by 1.5 (so, 150% of the poverty guideline level). Any income you have over that amount is considered "discretionary." For a single person in 2017 it was just over $18,000, for someone with a dependent it was in the $24,000 a year range. The student loan repayments would be calculated based on any income you had over that amount.
On most, if not all of these, you'd be hit with an IRS tax bill for the written-off amounts after the repayment period ends. However, if you are not in a financial situation to pay that bill (aka, you're technically insolvent), there are mechanisms for forgiveness of the tax debt.
It's definitely worth looking into. Also, if you are not working, you can get a hardship deferral (I think is the term) if you cannot make payments. (If you don't have income coming in, for heavens' sake, don't be making payments you don't need to be making!) If you are on the REPAYE program, the months you are not able to make a payment still count as "payments" so you remain in good standing, credit-wise.