EasyTransfer makes this simple. Or simpleish.
You'd need to build a packet format, something like:
struct SEND_DATA_STRUCTURE{
byte car_id;
unsigned int speed;
byte amps;
};
To prevent everyone talking at once, have the computer send a request for data by setting the car_id to the appropriate car_id, then wait a specific amount of time for the car to respond. Repeat ad nauseum.
Google "HM-TRP Telemetry" for a radio option. You can get them in pairs, one piece with a USB interface, so the computer side doesn't even need an arduino if you're prepared to write a program that will format the packets in the same manner as the EasyTransfer library (which is not hard to figure out). They are capable of transmitting around a mile line-of-sight.