There are really two issues here.
- Can/should the PTO break away from the school as an independent group and manage it's own funds? (Because right now, you're serving as a committee for the school.)
- Whatever happens, how can you arrange a better relationship where the parent group has input into fundraisers and the use of funds?
Your time to negotiate this is when the fundraising is planned. If the school is using parent volunteers to run the fundraisers (not to mention that it's most likely parents doing the buying), then
that's when you have the leverage.
I know it's hard, but try not to let it become adversarial. Start from the point that both sides want the same thing - to benefit the school and students. But if the parents are going to make this effort, then they want some input into how the funds are spent. Most importantly - put the agreement in writing. If possible, an agreement both sides sign. If nothing else, a write up of the meeting with your understanding of the discussion, that is sent to the principal.
I've come full circle on this issue, no longer believing it's automatically the "right" thing for a parent group to be independent. Certainly it's a good way to go, but there a lot of work and overhead with that status, and it's not for everyone. Being a committee and letting the school provide the treasury function can work well - but you still deserve input into the process.