I cant believe someone would say they couldnt afford a helmet. How could you afford a trials bike but not afford a helmet?
One of my trials riding friends a few years ago came off on some really little rocks near my house. He just fell backward after trying a move like we all do but he landed on both feet and kept going backwards.
He hit his head really hard on a pointed rock that we hadnt even looked at. He wasnt wearing a helmet and died from head trauma about 4 hours later.
Now tell me you cant afford one.