a 50/50 or 60/40 split is pretty standard with 60 % for you being a good deal. The fact that they charge per student also means that they will have a vested interest that your class does well.
You might want to look around. The rates can vary greatly, but they can also be dependent on how much work the host venue contributes to the arrangement. I’m doing a lot more workshops and classes outside my home gym now and it’s been surprising the variety of ways people charge.
At one place, I’m paid about 1/3 of what the company charges, but they advertise and sell spots on my behalf and all I have to do is show up and teach.
At the second place, I pay 33%, but they do zero marketing.
Another place, we co-market and the split is 50/50.
The best deal I’ve got lets me have the place for 2 hours for a very reasonable fee and I have unlimited upside income for the same flat rate. I can advertise on their facebook page but I can’t put signs up in their facility.