We give each classroom $200 to start the year. We have a couple of classes that have 2 part-time teachers, so it wouldn't be fair to give each teacher the full $200 each. We do not require receipts. They always tell us how much they appreciate it and are able to buy things for the classroom they might not have otherwise.
Our PFA gives each teacher $400 for the school year. Teachers appreciate it because they'd otherwise be taking money out of their own money for classroom supplies (to cover the parents who can't afford to or didn't bother to bring in their own supplies or classroom money).
We have over 100 teachers, they don't get anything for back to school! We do pay for all the student field trips, and pay for several in school programs during the year, as well as purchasing all of the playground and other outdoor equipment. We've been talking about doing a small amount for each grade next year that they can choose to use either for supplies, or for a grade level only program.
I find it bizarre that your parents are complaining about teachers getting money to buy classroom supplies. Do they think the teachers should be buying it out of their own pocket? Would they prefer to get a giant shopping list from their teacher at the start of the year? Or do their kids just not need pencils and paper?