try this
http://www.oople.com/forums/showthread.php?t=92862
this would be more competetive, than a rtr
however it's more about the driver than the cost of equipement in rallycross, the cars are all massively over powered and it all about calming down the setup to make it easier to drive, a trophy 3.5 or d8s would be good to have ago with.
enjoy it