The new X3 is pretty quick out of the box, but the DM1 Spec can be a solid purchase as well. Both will get you started, but updates are needed with both. Best buy may be the Serpent or Serpent RTR. The full car does not require many parts, the RTR may need a few parts.

X3 and DM1 will.

I am running the X3 and spent 3 years running the DM1, and have parts and set ups that help. You can find good deals on used DM1's for around $200 and some have the up grades. I have a roller if you are interested.