I Made a $20k Military Radio for $100 with Open Source Parts [video]

Where I work, we make complex industrial robots that incorporate multiple SBCs. The SBCs we use cost a bit more than $2K each, although you can buy functionally equivalent ones off of Amazon for about $200.

The reason that we go with the expensive ones over the cheap ones is that the expensive ones are hardened for use in very rough environments (electrically noisy, dirty, high temperature, high-vibration, subject to frequent physical shocks, etc.). The cost isn't for the computational abilities, it's for the ruggedness required to operate constantly in adverse environments for years on end. My guess is that the same thing is true for these military radios.