You won't know until your credit is run.
$80 down for awesome credit.
$608 for average.
Full price for no credit check.
Taxes due on full amount when you actually order or take possession of the phone on any credit level.
Prepaid is full price.
Perhaps you should consider postpaid if you have good credit. Postpaid offers EIP.
I know after x amount of time of on time payments there are positive remarks on your account and down payments may be reduced. You'll just have to check online or call or go to a store to know for sure.
Manage your T-Mobile account