Cheapest i've seen half decent backup phone or first up smart phone from a well known manufacturer.
This Boost Sony Xperia E Pre-Paid Smartphone has all the necessities to keep you in touch, with a 1GHz Snapdragon Processor and 512MB RAM, a 3.5" HVGA Display, a 3.2MP Camera with VGA video recording, 4GB of storage and a microSD slot offering up to 32GB expandable memory and audio filter technology via xLOUD, all running on the Android Jelly Bean operating system.
Stay in control of your data with the data usage app that helps you manage your costs and keeps your phone bill free from nasty surprises. You'll also be able to manage your battery thanks to the power management functionality.
With HD Voice* functionality, make yourself heard clearly to the person you are calling, cancelling out loud environments and background noises so clarity is consistent on both sides of the call.
Create your own playlists in no time and crank up the volume on the Xperia E, with the reputable WALKMAN app which provide xLOUD loudness enhancement and a graphic equaliser so you can tinker with your sound, your way.
Can vouch for all the above mentioned apps that i use on my Sony phone also.
Contact "Bagman" if you need to unlock the phone.
Just be careful, my sons xperia e wont connect to home wifi