How much does kendo lesson generally cost?
It depends entirely upon the size and setup of the dojo you are attending. Their membership fees will be based either per lesson or per time frame (yearly, half yearly, quarterly, monthly, weekly etc). Here in Sydney, my club charges $90 AUD/year or $50/6 months, which is super cheap, while other clubs charge $240-300/year, while I know of clubs in Australia that charge $10/session. They are generally costs to offset venue hire and admin costs, but be careful of those that charge excessive fees. Ask if you are not sure where all the money is spent upon as you will have the right to see financial documents if you are a paying member of the club.
