Honestly when it comes to something like that (a classic buggy) your best bet is to put it on ebay.
Price you get depends on the market which can be finicky. I've seen an original Yokomo Dogfighter go for close to 1k with a bunch of spares in great shape. But that was unique.
I think the car by itself would fetch between 200-300 dollars....
The radio, well, not much interest in classic radios from what I've seen...
JQ Products "Le Car" - 3 of them. Primary, back-up, and spares car
Bunch of "classic" Schumachers
Tamiya - Leopard 2A6, Tiger 1
HPI - Blitz