For the Half Assistantship, Maryland gives forgives the cost of five credits of tuition per semester, charges the remainder at in-state rates, gives you a stipend of around $6000 a year. If I remember correctly, this takes care of all tuition and fees except for about $2k a semester. Then its up to you to pay for living costs. So I believe you would save significantly over JHU, even with your funding.
My friend was chosen as an RFFG fellow. I think he has to decide this week if he accepts or declines, in which case an alternate will be chosen. He'll probably accept though (how do you turn down full tuition with $35k of stipend money over 2 years!?)