Smallest plan you can add it to is the $49 a month, so $59 a month with the phone. I went from a $56 a month plan with more data, down to this one which still includes 30GB and is more than enough for me and is month to month without a lock in period, so effectively only cost me 36 x $4, so $140 for an almost $700 phone.
Only catch is that if you cancel the plan before device is repaid, then you have to make remaining device payments at full price of device (so $20 per month instead of only $10).
What a rip off. Boost prepaid so much cheaper.