You mention the Mammoth or Savage, but what about the Mad Force at 700.00 just for the kit? and the LST which I think I saw a price for the Kit at almost 600.00.
I can get a savage ss kit for 360.00
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Wherever you got those prices from......RUN AWAY!!!!!!
Seriously though, you can get the Mad Force Kit for $300.81 and the Savage SS Kit for $339.99 at Tower Hobbies PLUS get $10 off more for purchases over $99. (that would pay for shipping).
The Mad Force wheelies on demand so your kid might have more fun w/ that, but they are both good trucks.