Direct from the Logitech website is £249, but alas they are also out of stock.
I think you could actually make some serious money if you buy up 20 or 30 top end wheels a few months before a GT release date and wack em on ebay unused after release. I remember the same problem with GT4 back when it came out and I wanted a wheel. I've seen used G25s and G27s going for over £300 on ebay the last week, and I saw a GT3 RS V2 go for over £500!
I'll have to remember it for the next GT game!