If you are adding on to your Aunt's family plan, then yes, it will be $9.99 to get added to her bucket of minutes, plus your data plan ($15 or $25), plus your text plan (unless they already pay for unlimited texts.) If they belong to one of the qualifying plans, you will be able to add, I think 10 'favorite' numbers (such as your family, still on Sprint) that don't draw from your regular minutes. Actually, I'm not sure if you get to add 10 yourself, or if that is for everyone on the family plan total. Worth looking in to though.
Edit: This is all assuming your Aunt already is on a family plan. If not, you will have to choose with her which plan you will share. Plans start at $59.99 for 550 shared minutes. This is $20/month more expensive than the cheapest $39.99 individual plan for 450 minutes.