They only have one plan, which is unlimited minutes, texts, 4G LTE data, plus a 50GB hot spot. The base price is $30/mo. with no contract. After coupon, the price for the first six months is $21/mo.
*** Note- you cannot port in an existing Sprint number.
The only other fees are a $3.50/mo. regulatory fee (for comparison, Mint charges roughly this, and Visible rolls it into their plan), and a one time $10 fee for a new SIM (these are free with Mint and Visible, I think).
They also sell phones starting at $30 with a plan. A "like new" iPhone 6S is $70, Samsung Galaxy J3 is $30.