I don't understand what money would be needed. The incubator? (I assume) If the school buys it, then the school owns it. Is that what you want or do you already own an incubator?
I'm assuming that the teacher doesn't want you do pay the extra power bill to run the 'bator 24/7 for 21 days. If you were going to keep the chickens at the school there would be expenses, but if you are supposed to take them home shortly after they hatch, then you already have what you need for chicks. So what expenses is your teacher expecting a 6th grader to pay for?
I'm assuming that the teacher doesn't want you do pay the extra power bill to run the 'bator 24/7 for 21 days. If you were going to keep the chickens at the school there would be expenses, but if you are supposed to take them home shortly after they hatch, then you already have what you need for chicks. So what expenses is your teacher expecting a 6th grader to pay for?