As you have a few years until he's old enough to start Karting then it shouldn't be too expensive to get him started. If he starts young and is good then financial backing would aid his career. I'm not sure how well supported Karting is in the US compared to Europe. My son is 6 and he's interested in trying in the next year once we can afford a Kart etc. My friends son has started at a karting School at the age of 7 and he doesn't have a Kart of his own yet, but once he's ready to race then it shouldn't be very expensive, especially if you or a friend/family member is capable of maintaining the Kart. Just travel costs, entry fee's and some maintenance of the Kart will be your initial costs. If he's good enough then sponsorship will come his way and that will help towards progressing into cars.