I dont know if these devices are available worldwide, but we, Indonesian, have 2 cheap devices exactly for that. ZTE B860H V5 and HG680FJ. It’s like $10 without remote, and another $1 for the remote.
It came locked by one of our ISP, but you can easily unlock it and put anything you want in it. Linux, OpenWRT, or just regular Android TV. ROM choices are limitless.