Perhaps international wheeling and dealing just isn't for me. The link that both Hodder and Mark gave me led to the same factory, which advertises these starting at $0.5, which would be a bargain, but when I asked for a quotation for 200 units, shipped FOB (which is just about the cheapest way to import this sort of stuff) I was quoted $3.0 each, so a product cost of $600 plus shipping, insurance etc etc. Unless the factory can do a lot better than that, I shan't be bothering.
Les