Are you a beginner?
See cost wise: used car<new car<kit
So If you are a beginner go for a race oriented RTR that falls in your budget. I am personally wary of used cars.
Then you have to decide whether you want to go for buggy or truggy. Both have different feel.
This site offers Ofna/Hong nor/Jammin race oriented buggies & truggies:
http://www.joyrisinghobby.com All this is for 1/8 scale vehicles which are the real deal.