Cheapest way to join a gym (sports club)

If you work for a IT company,
you may belong TJK (東京情報サービス産業健康保険組合) which is a health insurance organization.
If so, you can use KONAMI sports club only below prices for 1 time.
Category 1 : 440 Yen
Category 2 : 560 Yen
Category 3 : 680 Yen
Category 4 : 928 Yen
You can buy 4 times coupon which include extra 1 more time.
 As far as I know, it is the cheapest price.