Reference
How To - Needs - Wants - Documents
The only real requirements for racing are:
1. A 40cc or 50cc pocketbike (depending on race class) in good working order.
2. Protective gear (at a minimum): a helmet with eye protection, leather gloves, a jacket with elbow protection, knee pads/sliders and footwear that will cover and protect your ankles.
3. You must register the morning of the race and have your bike inspected before you will be allowed on the track.
4. If you are under 18 you must have your parent or guardian sign the waivers for you.
5. See the rules for further details.

Practices are typically free but protective gear is still required to be able to ride.