Keep in mind that you can defer the payments for the first six months after completing your training. Then if you participate in ATP’s Tuition Assistance program that can reduce your monthly loan payment by up to $500 per month, which is a huge help. That money will continue through your first year of employment at the airlines.
Even still though, $900 or even $400 is a sizeable payment, it will take some sacrifices on your end to be able to make the payments. You might have to give up some things, but I think you will find it is worth it, I certainly did. Bear in mind that missing a payment is not really an option, especially since your grandfather’s credit score will be tied directly to your account just like it were his.