Wouldn’t that be a NUC? I see lightly used i3’s go for about €150 (4GB+SSD), so no need to mess with an underpowered ARM SBC.
Over time, the ARM chips will gain enough power to run Roon Core, but that moment is still a few years off – and I don’t think powerful chips like the A-series that Apple produces would have any price advantage.
But we’ll see.