RE: Can't decide on 1/8th scale truggy
I would recommend an 8T 2.0 RTR for your son, and an 8T 2.0 kit for you. The RTR will have your starter box, and with the kit you can get a more race-oriented(i.e. fuel-friendly..) race engine.
Losi, IMO, just has great value-for-money. Especially with the RTR, where, as I mentioned, you'll have the starterbox AND a good radio. The engine is good too IMO - will be fast as hell.., but thirsty on fuel.
So the Losis, paired that way, would be a neat compromise between going with just kits or just RTR's.. One of each, and for starters you can just share the starterbox..
As an engine for the kit, there are more and more great budget racing engines around - Go GXR 5-port, Alpha Z or S 852, Jammin JPX 21, Werks B5, etc.. Keep an eye out on e-bay, etc.. and you can find some decent servos, tires, whatever else you need...