Re: signing a contract
In our dojo you can test four weeks for free. You don't have to sign anything in that time. And we tend to see "four weeks" generous.
If you want to join the dojo, you sign a contract. It says, that the membership lasts at least one year. After that year you can resign every three months.
Contribution is 12 € (~ 14,71 $) per month.
Most dojo I know have such a "at least one year"-clause.