DISCLAIMER: This process will overwrite the current Android ROM on your TV box. I have tested these steps on my own devices, but I am not responsible if you damage or brick your device. Verify the ROM will work on your device before starting and make sure to backup any data you do not want to lose before proceeding.
I love the idea of the Raspberry Pi, but there are some cheaper alternative single board computers that offer a similar experience for a fraction of the cost. While the community support isn't quite what it is for the Pi, there are a ton of projects you can accomplish on the cheap with these little hidden gems. Keep an eye on AliExpress and Amazon and you can find SBC's sporting quad core ARM process with 2-4 GB of RAM for under $30, including a power supply and IR remote control.
The box used in this video is a M8S (RK3288) I picked up on eBay for $15.99 shipped. It sports a Quad Core Rockchip RK3288 @ 1.8GHz and 2 GB of DDR3 RAM.
https://www.ebay.com/itm/264726126644
!! Warnings !!
This will remove the Android OS that came with the device. Make sure you have a backup of the Android image before proceeding in case you want to revert to the stock Android image in the future. On my box the wifi and remote control did not function and the wired networking was really slow.