Which is the cheapest hobby??

Tweet

According to me the cheapest hobby is singing... One can sing anytime, anywhere... without spending money... Singing and collecting coins are my hobbies since my childhood days. Iam not a professional singer but I sing when Iam in the kitchen, bathroom, work place...anywhere. I sing when Iam happy as well as sad. I havent spend any amount of money in it..On the other hand coin collection is a bit costly and time consuming hobby for me... I know many people will have different opinions and I just wanna know which is the cheapest hobby??