Network admins are network admins. And IT people with Linux experience doesn't have to be expensier than Windows IT people. IT people here study both, salaries are shitty everywhere.
My high school (2005 IIRC) had guadalinex [1] on all computers, with a 2:1 student to computer ratio and no in house IT. Students basically use Firefox, OpenOffice and some other apps for math and psychics, there's not a lot that can go wrong and nothing is so important that you need a person always on site.
I would expect the cost per seat (os + office at least) to be in the order of $100 if there are a lot of discounts involved, possibly as high as $400. That's a lot of money upfront.
It might not save in the support cost, I agree - but barring a (potentially uncomfortable) transition period, it shouldn't cost more either.
It is my experience (from industry) that a competent Linux admin can support about 10 times as many machines as a competent Windows admin, but only costs 2-3 times as much; However, competent linux admins are much harder to find.
My high school (2005 IIRC) had guadalinex [1] on all computers, with a 2:1 student to computer ratio and no in house IT. Students basically use Firefox, OpenOffice and some other apps for math and psychics, there's not a lot that can go wrong and nothing is so important that you need a person always on site.
[1] http://www.guadalinex.org/