One thing I know about Special Ed funding is that it is mandated by law. If there is a child who is profoundly autistic (for example) and needs a 1:1 aide to be able to be in the classroom, that has to be paid for and set up by law. That money to cover that comes out of the general ed fund. Or if the child is blind and needs everything translated into Braille, etc. That must be done and paid for.
To me, it would be cheaper/better in the long run to find out why kids have these disabilities and work early on to prevent them. For example, pay for early intervention to help at-risk autistic children not become profoundly autistic (you get the idea).
My son is very gifted and hearing impaired. He's a "special Ed" student- the county bought him an FM system for $1500. The teacher wears a Mike and it puts her voice wirelessly into his hearing aid. I was invited to join the county's board of education committee for Special Ed, which is how I have learned about all of this.