I recommend finding the dates of the Sumo tournaments online. To see a sumo match without breaking the bank, arrive at the stadium at 10 am (or earlier) the morning of the match. You will then stand in the most organized rush ticket line you’ve ever seen. Everyone stands quietly and orderly and proceeds in the queue. They’ll then sell all the remaining tickets for the day at around $20 a piece. Just be sure to get there early to avoid disappointment!
P.S. One of the excellent things about sumo matches is that you can bring in your own food and drink!