I didn't expect I'd have to explain the existence of LibreElec in LibreElec forums: It is there because people want to use their hardware just for kodi without wasting memory and system resources for an opterating system they don't use (and maybe don't trust) for any other porpose than running kodi and want to use well maintained upstream software with continuous security- + bugfixes.
I really don't understand why it would be required to have support from the vendor of a android box for furture support: LibreElec is a complete own operating system which doesn't depend on any other thing then the hardware of the device - that means: if the device (or a similar one) is supported in the upstream kernel - there will be support for the device as well for ages. Because tv boxes are often very similar and Tanix TX6 is supported in upstream kernel and has offical LibreElec support, I think it will work on other tv box as well (especially on Tanix TX6 mini) or can be made working with little effort.
When it comes to pricing:
RPi4 basic version (2G) : 40 US$ (most pepole will need HDMI adapters + usb-c power supply)
PINE H64 basic version (2G): 36 US$
PINE rock64 basic version (1G): 25 US$ (2G version available at 35 US$)
Both H64 and rock64 can be ordered at amazon at slighly higher prices (which is also true for RPi4).
I really do not think that RPi4 is the most competetive (with neither pricing nor hardware (and current software) capailities) when it comes to mediacenter software and there has been lots of efforts by the community to make it work on Allwiner (and Rockchip) with FOSS: that should be considered here if somebody asks which device is the best to use for LibreElec - also the question of future support prefers the these SoCs as support for them comes exclusively from upstream kernel.