The cost there is 100 for 6 laps on the normal carts (some 9 hp i think)
150 for 6 laps on the slightly better carts (karts 8 and 9 i think)
200 for 6 on the superkarts (10.5hp+) --> Trust me, these are TOTALLY worth it. Wont feel like driving the normal ones after driving these.. The feel..sound..power..braking..handling.. everything is just brilliant!