There is no way for us to know that.
Vet prices so much from place to place. The best thing to do is see how is foot is doing in the morning. If it's not tender, and he's romping around just fine, you shouldn't worry. If it's tender, you should ask your mom to take him to the vet to make sure it's not broken. But here's some additional thoughts:
If it is tender in the morning, I don't know what time you need to be at school, but many vets open at 7:00 or 8:00. You can call from home and tell them the situation. You're 13, but your cat's foot was stepped on and he's acting like it still hurts, and you're callling because you want to find out information before you go to your mom. Adults really respect this kind of thing, and I'm sure they'll be very helpful. Ask
How much does a vet visit cost? If the vet thinks a bone was broken, how much does an X-ray cost? If the foot is sprained, would it need to be wrapped? How much does that cost? Are there payment plans available? Then just thank them so much for their time.
That way you can go to your mom armed with all the information.
If a vet isn't open before you have to go to school, take the number with you and have change for the phone.
And you may want to mention to your mom before you go to school that this happened to your kitty. She may want to help any way.