AT&T data plan what's the lowest data plan?

I want to get the new iphone and I've never had a smartphone with a data plan. My parents don't have smartphones either so it would just be me getting the data plan how much would the lowest data plan cost?

It depends on how exactly your plan is set up (I.e. Family plan, or each separate)
I have the lowest data plan (300mb) from AT&T, practically unlimited minutes ( which are shared with 3 other phones on the plan, and unlimited data.
It's about $30 a month.