There are so many different ways you could build this into an RC platform, it all depends on your resources. If you have enough money for a vex kit with the programming tool (and you want autonomous), I would definitely go with that though.
Searching the rest of the internet for info on how to do stuff like this has often ended well for me, and I would suggest it if you haven't been there already. There are DIY people everywhere.
EDIT: Forgot to mention, if you have an old rc vehicle, and you are willing to let it die, figure out how it works and convert its controls to suit your purpose (nondestructive disassembly is important here, I made that mistake a while ago

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