How much does ju jitsu cost a month?

This can vary depending on your club. Some classes only charge £20-£25 a month whilst others may pay more. Get in touch with your local Sensei and ask them. Don't forget though there may be other charges such as: Ju-jitsu licence and insurance and the price of the Gi's (Uniforms) and sometime the price of the gradings. But as I said, it depends on the club, so give them an ask!