Once you pay for trademark registration and the process is finalized, your trademark is valid for ten years. The price for the registration consists of the government fees charged by the respective IP office and the service fees paid to the law firm representing you (if you don't file your application yourself). During the ten years starting from the registration date, no maintenance is required, and no extra fees are charged.
However, if you wish to keep your registration alive, you should renew your trademark before the ten years are up. The renewal fees vary depending on the specific jurisdiction, as every IP office has its own fee structure.
There is one exception which is the US. Here, you have to prove that you are using your goods/services in commerce between the 5th and the 6th year from the registration date. You will be asked to submit the evidence to the USPTO, which also involves paying follow-up fees.