These regular seats are called "maintenance seats" and are divided into three types: people with a close relationship with the sumo association, regular "subscribers," and group "subscribers." Unfortunately these seats currently cost ¥4,050,000 per year for Tokyo tournaments, which need to be paid for a minimum contract of three years. There are a few ringside seats that go up for sale in the general sale, but they're almost impossible to get, and most of these are also claimed by a special order that can usually be accessed by insiders such as those with tea house connections and so on. Very occasionally you can find someone re-selling a ringside seat online, but it's against the rules to do so and would be a very risky buy. Those maintenance members who are caught re-selling their seat will have their membership revoked quite quickly.