It will depend on whether you buy a completely new or used setup. You can find some sweet deals on used and not abused chassis in the for sale forum. I picked up 2 XRay T3'12s for about $225 each for USGT and VTA builds.
TC - New chassis, motor, servo and ESC can easily set you back $600 or a lot more easily. High end gear, high end prices. But, you can always go to VTA and USGT if 17.5, 13.5 or mod isn't for you.
VTA or USGT- see "TC", but get a used quality durable chassis, like XRay and the ESCs tend to be a lot cheaper. Your still talking between $400 and $500 to get a car on the track.
Cheap and durable racing:
GT12 (huge in the UK) and Legends. Both of these classes don't get talked about much, but are a lot of fun and cheap to run.
The only car I don't have is a Legends chassis.