Some Chase cards now have a targeted Mint Mobile offer that gives you $10 back with any purchase amount. If you’re not familiar with Chase Offers, see: Introduction to Chase Offers
According to reader wangbo, you can buy start kits in the Mint Mobile app for just $5 each. That means you can effectively come out $5 ahead.
If you have multiple Chase cards, check all of them. Similar offers also appear on BofA cards. In addition, Regions Bank, Suntrust Bank, BBVA, BB&T, PNC, Columbia Bank, Beneficial Bank, and Christian Community CU all use the same offer backend system, so if you have cards from those banks, check to see whether this offer is available there as well.