Sure, you can get a fun RC car for $100, but if you want to compete, it's going to cost you a lot more than that. Lets say you want to race 1/10th Electric cars. Using really approximate figures, you could spend $200-400 on a chassis, $50-300 on a speed controller, $100 or so on a motor, $150 or so on a few batteries, $100 on a battery charger, $100 on a transmitter, however much for receiver, servos, few sets of tires, spare parts etc etc etc. It's been 10 or 12 years since I've been in the RC scene, so I don't know how much you need to spend to compete now, but even if you just look at the basic costs there you're looking at close to $1000 once you take all the little things into account. If you want to buy secondhand I'm sure you could get set up for a fair bit less, but at the same time I'm sure a lot of the top guys spend thousands....