pops serpent makes an vrc adapter that is supposed to allow you to use your own transmitter on your PC. I for the life of me can never find it though. Supposedly with this, you can use your transmitter for anything that a steering wheel or joystick is used for in other games as well.
Traxxas also sells a cheap pistol style controller you can buy from rcboyz on ebay for 50 bucks but it's not as good as the futaba one that comes with real race.