It's not really complicated with a small program. Students know what they are supposed to pay, and pay that amount. I can easily remember what the correct amount is for each of my few students. With a larger program, you'd need software that allows this type of approach. I'm also non-commercial (in that I'm not in this to make money - most of the fees go back into equipment and such), which might be why I'm okay with never raising fees for existing students. If I opened a school, I don't know that I could stick to that principle.