Actually, even cheaper, might be a Pico (from the Raspberry Pi Foundation). It's meant for embedded devices, so not meant to have a screen or anything, but you CAN add a touch screen for a few bucks. I'm sure you could probably add a disk controller for a few bucks too. The nice thing about it is that it's very small, not very powerful, so not a lot of cooling needed, and very cost effective. I envision a Spin Rite dongle that you could connect to any PC... and it would work like a VM to house the low level code in a way it can work with any other PC.
@Steve, how about this for an idea...? I know you went the way of the RTOS so you could have a Windows feel... but maybe you don't need to deal with booting on specific PCs and just built an API for talking to a "dongle" and a Windows user of said API as the example that the FOSS community could port to Mac's, Linux and phones and tablets.