I just came across this article on Hackaday: A Xilinx Zynq Linux FPGA Board For Under $20? The Windfall Of Decommissioned Crypto Mining | Hackaday
These are basically cheap secondhand controller boards with Zynq-7010s, similar to the Z7020 in a roboRIO. These boards should definitely be able to run the FRC roboRIO OS; they may or may not be able to use the FRC FPGA image (the difference between the 7010 and 7020 is a bigger Artix). If not, it should be possible to create a smaller FPGA image with less functionality.
I just ordered a handful. When they arrive in a month or so, I’ll post updates. For our team, at least, being able to run robot code on a $10 dev board instead of a $500 roboRIO would be a huge benefit.