Super cheap also means super cheap software, and no chance to install other OS's. Something under 50$ should be OK.
Right, you can find some Android boxes which can run 8K video on pre-installed Kodi for around $40 (if you filter out all the really cheap crap), and they are ready to go (with remote, power supply etc).
But still you may find hardware issues after a year, or updating to latest Kodi will be impossible etc.
On the other hand with RPi4 you need:
- RPi4 2GB RAM = $35
- IR Remote = $15
- MicroSD 1GB = $2
- Power Supply 15W = $12
- Micro HDMI to HDMI Adapter = $9
- Alu case = $12
So in total around $85.
Buying some $40 android player and put it in the trash after 2 years when it breaks and buy again another one for $40 might not be bad strategy after all