Tamiya DT02
Hi can't help you but I just set up a Tamiya DT02 chassis ( Holiday Buggy, Sand Viper, Sand Rover & Etc) For my mates 6 yr old & he loves it. Comes with ESC & motor.
They can really take a pounding as we run them at Boondal with a 13t combo.
Price around $85 to $100 + post from Stella.
Other Choice is a Hobby King sc10 truck in kit form for $100 posted from the Australian warehouse . Add your own electrics. A bloke just did that for his son at our meets.
Food for thought.