We do not present our budget until the second meeting, either, to get a sense of what the school year is going to be like.
The board pretty much sets the budget, but we only allocate based on a very conservative estimate of what we will take in, and then we 'reserve' some of that, too.
The amounts in our budget are for things like grade level allocations, individual teacher allocations, PE, art, etc. Things over and above these items can be requested and debated/voted on by the general membership.
This way, we give a say to anyone who wants a say without haggling over the most basic of things. That's the theory, anyway, and it worked out last year.
Also, if we cover the basics with our catalog sale, we can say that later fund raisers are going to specific causes that have been requested -- computer equipment for the lab or science materials. (We can approve/commit to funding something even though we don't have the $$ and then raise and save for it.)
Technically, the budget itself can be amended through motions at the budget meeting, but our membership is not that engaged, thank goodness.