You could call around and check the sites, like you already received in the answers.
I called around and checked the gyms in my area. To give everyone a chance, I started with a fee on the low side. To be fair to my fellow trainers in the area, I increase it each year to be closer to the going rate.
another important distinction is whether you are employed at a gym or are on your own. A lot of gyms take a substantial cut from what the client pays, and it often seems outrageous.
If you are looking for such an employment situation, you need to make yourself knowledgeable what the gym will provide to you in return. Not knowing your situation, let’s say you are a novice trainer. A gym often provides exposure to potential clients, and you have no overhead for travel or the purchase of equipment.