Here's the latest Cato Institute video on education. The link will get you to a PDF explaining the methodology used to get the numbers in the video.
If you need a standard for comparison on this, you can send a fairly low-maintenance kid to Texas A and M, one of the best schools in the state, get her in classes, buy books, rent a dorm/apartment, and keep the kid fed for around $16,000.00 per year.
You can put a child in Fort Worth Country Day, or Trinity Valley, two of Fort Worth's finest private academies, for somewhere around $16,000.
Please allow me to counter a few objections to privatizing our school system tomorrow:
1) Private schools don't have to accept anyone who shows up (special needs kids, for example).
Well, we're currently spending a QUARTER OF A MILLION DOLLARS per classroom. According to the Cato Institute, it's double that in D.C. All that money is going someplace, and it isn't to teachers. There is some slack to be found in the savings for special schools for kids with special needs.
2) Some parents, if given vouchers, would not make good choices for their children.
Ok, think of the worst school choice a Fort Worth parent could make.
The defense rests.