Depends on how many sessions you have that week. Straight from the wiki:
Upkeep budget: If the gym is dirty, fighters will lose morale when they train at your gym. This will have managers looking elsewhere for a well maintained gym, so make sure you set the upkeep budget at an appropriate level to maintain a clean gym. You need to spend $1 per fighter training session. So if you have 100 fighters at your gym, the most fighter training sessions per week that your fighters could have is 1200 (100 x 6 days x 2 sessions per day). A fighter training session is only counted if the fighter actually trains, so if they're set to no training for that session, it will not count towards this $1 per session total.