RE: Cheapest KIT
I dont know about kits... but most cars come with an engine...
The DTX Evader (i highly recommend them, but then again ive never owned another nitro car), runs for about 200 w/o radio, and about 240-250 RTR
Tower hobbies is having a sale, so you'll get 25-30 dollars back too, depending on what you buy with it, if anything.