In reply to Bingers:
Can we mention the C word?
C*x and Dara O'Brainy are on the cover of the Radio Times this week wearing a pair, so expect them to sell quickly now. I think they'll be in Skye getting maximum coverage, depends on your location.
check fleabay, I found a couple of sellers doing those quantities, about £1 a piece. I can send a link if you want. They aren't professional astronomy sellers though, more like Del Boys with an eye (geddit) for an opportunity, I think. Mine came from someone styled Deano or Damo or somesuch confidence inspiring affectation. I think you'd have to order them yourself as the school wouldn't order from them.
Do you need 250 pairs? It's a big investment if it's cloudy and because it's a (relatively) slow event. Most of the ones on offer use Baader ND 5.0 film much better than the Mylar used in 1999, which was prone to scratching and pinholing and could be more dangerous if passed from person to person.
Out of interest what's the school said? I'm in touch with 2 primaries and they showed initial enthusiasm but it's all gone a bit quiet, H+S concerns maybe?
For indirect viewing you can use pinhole projectors or the telescope idea above or you could use a digital camera and make a filter. There is good film available but it had all sold out last week, I just got an order in, but I've had mails from a couple of suppliers saying more has hit the channel this week so you can get an A4 sheet for £20ish.
If not you can always cut up some of your 250 glasses and make a filter to fit over a camera lens (securely taped on). I did that last time and it's very effective, plus the bonus of no direct viewing. If you have LiveView you could put it on a laptop or projector.