[trogggy]

- What is the lowest cost solution that will meet the requirements above that others would recommend?
- Secondly, if i'm running Libreelec, is there any downside to having one of these cheap chinese boxes? Should everything just work?

I think the best thing you can do is to have a look on the libreelec site, read the s905 thread and pick out a box people confirm is working well with kszaq's libreelec.
Even better, after that have a look on freaktab and amlinuxmedia.com (you have to register to view there), again read the threads, look for boxes that people are recommending.