I'd certainly recommend [Raptor Systems] to business owners but I'm looking for something for my own modest use and I don't have that kind of budget.
This is certainly reasonable.
I've alow followed Carefully coreboot and Libreboot hardware compatibility throughout the years but I'm wary of second hand electronics.
Well there are still some systems which would count towards this, for example the ASUS C201 has a Rockchip 3288 comes with Coreboot, and I believe can still be purchased new.
I'm more interested in the i.MX6 platform.
I did look into specifics of this for a while, but I've unfortunately lost most of my research. The only thing I can recall was that there were many very affordable SolidRun CuBox-i4Pro available second hand at the time I was looking. This seems to not be very relevant given your early mentioned preferences. I do wish you best of luck in finding a preferable model though.