Every year Valentino Rossi (among others) presents the world with his new custom race helmet for the season. He also tends to have a special helmet for his home track.
I love the idea of having a custom helmet.
It looks amazing. It stands out. It gives you a more professional look compared to another Rossi helmet.
The reason that most riders don't have a custom helmet is simple ... cost.
A high end helmet (one that I would consider suitable for racing) is going to run you north of $500.00. The really good ones that have the more advanced features (and arguably are more protective) are close to or exceed $1,000.00.
Once you have the helmet then you add in the cost of the custom design and applying that design to the helmet. That can run you *another* $1,000.00 or more.
As a racer I tend to go through 1-3 helmets per year. Some years I don't have a crash that damages my helmet but other years it seems all I am doing is hitting my helmet.