...cheapest Sigma 18-200 lens for Nikon D50?

Kentish

Ever since I bought my Nikon D50 a few months ago I have been wanting to replace the 18-55 mm kit lens with a wider range zoom, specifically a 18-200 mm one. As there is no way I can afford the Nikon version (costs more than I paid for the camera!), I've had my eye on the Sigma one. However, the cheapest I've seen it for is £235 +£7.90 p&p from PixMania - does anybody know if it can be had for substantially less, without having to resort to eBay?

I've got some overseas travel booked for this year (US, Australia) so I would also be interested to know if there are any duty free bargains to be had.

Thanks...