Cat 777D Mining Truck

[JensR]

Tom might be able to "switch" the ESC.
If the radio sets the servo full left or full right, this corresponds to up (forward) or down (reverse) with the ESC.
If the command from the receiver is not +100% and -100%, but +100% and 0%, a switch/relay like you suggested would be necessary, but I couldn't find whether or not the switch needs +100% and -100% to switch - if so, you have gained nothing (or at best a few bucks) over the ESC solution.