1)What helmet do you use?
Lazer Mamba XC

2)What did you pay for it?
Hmm.. If I recall correctly it was ~ $80 (sign of a good purchase)

3)And when/what will make you decide to replace it?
This was a helmet that replaced a totaled helmet in a MTB-ing accident that landed me in hospital with concussion.. My helmet, no doubt, saved my life... To answer the question: When it is ~3 years old, or showing signs of wear, or takes a serious blow... whatever comes first...

and no.. I do not ride without a helmet.. My brain is my number one work tool.. no way on the planet I want it traveling at 20 miles an hour, a meter away from a stationary, hard, totally immovable object (called the ground)