"The fastest SBC at CPU tasks priced below $100 is the Raspberry Pi."
The Odroid N2+ costs $79 and is over twice as fast as the Pi4.
The Khadas Vim3 costs $100 and is about 30-40% faster than the Pi4.
The number of SBC boards out there is becoming huge; although the PI price has dropped significantly wrt performance and features (especially RAM), there's a lot of comeptition, and it's growing.
It uses an Amlogic S922X aka the G12B. Support is generally pretty good, there's a dedicated community that has been very active pushing upstream[1].
Except the ARM G51 Bifrost gpu, which has only recently started to see viability[2] thanks to one hacker's reverse engineering. If you want to read a lot of words, there's a status report from the libreeelec Kodi-based media player distribution distribution that's a year old, that lays out a lot of what needs be done, from a very video-intense perspective[3]; this is before recent reverse engineering efforts, & largely discusses uses closed proprietary blobs, but still interesting. Most recently & very interestingly, there are signs that ARM itself may be willing to start helping out the reverse engineered development[4], which would be a new potentially interesting state of affairs.
According to the Armbian (one distro to support them all:^) page, mainline kernel support is complete, although they say there still could be some network problems. From what I read on their forum, the Hardkernel Ubuntu-based image is currently more stable than the Armbian one.
That's indeed much faster than the Pi4. Do you know the state of kernel support for that board?