How much is metro pcs monthly 3G data?

I have an unlocked iPhone 4 and I want to go activate it for metro pcs since they do that now. I'm currently in a family plan and we all share only 500 mb of 4g So I don't mind having a 3G phone. But how much would that cost monthly? Will I still be able to be in the family plan? Will the 3G be unlimited?

I'm trying to find the same answer --- lol but iphone 4 is not 3g so therefore your paying about 60 a month