^^ It depends what you're going to do with it. Racing or bashing?
If you're thinking racing, then you'll need at least-

Clutch basket= $35
Sway bars= $35
Racing tires= $45 (4)

Diff oils= 5k rear, 10k, or 20k or 30k front $15

This should get you started in the beginner 4wd sct class at most places.
The problem with the rtr is the motor, I don't think 550 4-pole motor is ROAR legal at this point, so not sure if you can race it...