Deal: Apple iPhone SE now $240 off at Boost and Virgin Mobile37
While both Boost and Virgin are offering their iPhones off contract, the handsets are not unlocked. It looks like you can unlock them for free only after using them for at least 12 months on Boost or Virgin (on plans starting at $35 per month). Another thing to note is that the iPhone SE units available on Boost and Virgin Mobile are not suitable for use on Verizon and AT&T (as they're missing essential LTE bands), but they should work perfectly fine on Sprint and T-Mobile.
As a reminder, Apple is currently selling the iPhone SE 32 GB for $399, and the iPhone SE 128 GB for $499, though these prices get you fully unlocked devices.
sources: Boost Mobile (iPhone SE 32 GB, iPhone SE 128 GB), Virgin Mobile