in the store the hpi set is about 18.00, I've seen them on ebay for 12.99.
Depending on what battery setup you have, you'll need to relearn how to brake again. I did the dual disk upgrade about 2 weeks ago and loved it, when the brakes are cool, it would flip the thing over if you hit the brakes! But after driving for a bit it would just stop on a dime without flipping...
BUT! just a few days ago I upgraded the battery pack from the 4.8v (4 AA batteries) to the 6.0v rechargable pack and HOLY COW what a difference, I'm backing the brake adjustment off because EVERY time I hit the brakes it flips. If your going more than a few MPH it will flip and land back on its wheels. So I wonder if a single disk and a 6.0v system wouldn't be just fine? the dual disk definatly work better. Maybe it needs ABS (anti-lock brakes) LOL