Most people that race rc cars are petrol heads that would race real cars if there were able to but just can't. RC racing gives a similar type of enjoyment (much smaller though) to kart racing but is much less expensive and less dangerous.

Firstly you'll need a speed controller ($100-$350) and then you'll need some radio gear ($100-550). If you think you'll be in rc for a while then spend as much as you can on a radio (300 or so will get you a decent one). you'll only need a brushed speedo for 540 (150 will get a good speedo) but when/if you jump up to stock you'll need a brushless speedo (300). It all really depends on how long you think you'll be staying in rc.
Drew.