There's probably scope for reducing staff at high schools, but don't kid yourself that technology is going to provide some magic reduction in the cost of primary education.
Edited to add: I think that making high school more like college in terms of giving kids autonomy and opportunities to do real-world types of activities outside of school would be a great idea, and conceivably could both lower the cost of running schools and increase the value of schools. But this requires much more than technology to enact, there is also an huge cultural and societal component to deal with.
At the end of the day I just see things like the Khan Academy introducing a paradigm shift in education, allowing us to think about entirely new institutions for educating young children. The idea that we need to keep 19th century education styles in the 21st century is just mind boggling to me.
You might hope that if you managed to replace some of what teachers do with technology you could pay the childcare people less. But it's not like teachers get paid huge amounts of money today. So I'm not sure how much scope you really have for cost-cutting there.
My view is that education is expensive, and growing more expensive, primarily because the field hasn't seen the kind of productivity increases that the rest of the economy has. Some of that might be due to conservatism regarding technology among educators. But a lot of it is simply that kids require hands-on supervision, there is maximum "student-to-adult" ratio that you can't really go over, and so inevitably education costs are going to rise faster than other costs. It's part of the price we pay for a technologically sophisticated economy.