From the Los Altos School District 2011-12 budget, total expenditures are $41,154,965 (from the table at the top of p. 4), and the projected total enrollment is 4460 (from the last sentence on p. 4). Dividing the two yields $9228/student for the year.
From the Bullis-Purissima Elementary School Foundation web site, Bullis Charter School spends $11,131/student.
That's a difference of $1903/student or 20.6%.
Thus, I would appreciate it if BCS supports would stop claiming that the LASD and BCS spend "about the same amount" on each student, or that the $5000 "suggested donation" is simply to "make up the gap". These assertions are simply not true.
I also want to note that I am making no attempt to drill into the different categories or line items to compare and contrast how LASD and BCS spends that money differently. That is a separate post. The point of this post is simple: BCS spends over 20% more on each student each year compared with students in LASD's traditional public schools.