RTR's are ok for a novice class, something you are running just to have a good time, and be with your friends bashing about.
Just like any other form of racing, or hobby for that matter. Pay more up front as your initial investment is always going to be your biggest, and do it right once. There are however good deals to be had from buying used parts on here. Just do your research first. Research the part, research the seller, view the imagaes, then make a concious decision.
If you are buying a RTR to be a competitive racer, you will make your initial investment twice, once to buy the RTR to realize it is anything but competitive, then a second time to replace everything to be competitive.