Honestly, you may be better off just plunking down the money on a kit. I think Mugen is pretty popular the vehicle performs. Also, I believe the parts may be cheaper than what the kyosho costs.
Maybe look on ebay for a used Mugen roller and then buy the engine new. You can always tear down the roller and rebuild it.
I think however unless you know the guy who had the vehicle and his breakin and motor maintenance techniques, best to get the motor brand new.