Cost of special education in public schools?

This weekend there was a large article in our local paper about the cost of special education in schools within my state. At a time when schools are being forced to cut teachers, cut extra-curricular programs, and ask local voters for more revenue, they are being required to spend huge amounts of money on special education. The article cites the average annual cost to teach a student in the state at about $9,000 and the average annual cost for a student using special education services at about $25,000. They seemed to very loosely define "special education" from everyone with a minor learning difference to those with severe emotional, behavioral, and/or cognitive problems. A few students with the most severe problems cost a school district upwards of $150,000/year the educate.

While I would not advocate eliminating special education, I want to know if there are reasonable limits that should be put on how much money is spent to educate a single student? Where do we draw the line between special education funding and funding for the education of all of our students? I would agree that special education greatly helps a significant number of students to reach their fullest potential but how can we ensure that all students are able to reach their fullest potential?