If you want to save money, you should look for a used helmet. However, the rule of quality over price should apply when buying a riding helmet, as it can save your life in an emergency.
The problem with used riding helmets is that you don't know if anyone has ever fallen with it, exactly how old the helmet is or how it has been stored over the years.
However, these factors can play a big role in the safety and functionality of the helmet. Only with newly purchased, good quality helmets can you be sure that they will do their job and protect your head.
A layman cannot tell whether there is damage to the material, for example, and whether the helmet even still complies with the current safety regulations. In addition, older models are usually inferior to the newer ones in terms of comfort and safety. Therefore, buying a used riding helmet is not worthwhile.
On the contrary, it can even be dangerous for your health.