Bus lengths

The maximum bus length for a CAN network depends on the bit rate used. It is required that the signal has time to travel to the most remote node and back again before the bit is sampled.

Bus length (m)	Maximum bit rate (bit/s)
40	1 Mbit/s
100	500 kbit/s
200	250 kpit/s
500	125 kbit/s
6000	10 kbit/s

ISO 11898 - impedance of the cable 120 +- 12 ohms (twisted par, shielded or unshielded)
Might be hard to find a cable with that impedance for cheap anyway :-S