Having said that, I've just noticed that Maplin are selling a wireless USB weather station kit for £49.99 - it seems to do all of the usual things including rainfall and humidity, wind speed and direction, etc. and was apparently priced at £125 previously. No idea when the offer ends, I had my hands full of shopping so didn't want to stop to take a closer look.
later Well, according to the Maplin web site that one is currently full priced and out of stock, and the one that's on offer isn't designed to interface with a computer - but that's definitely not what my local shop had, they were selling the USB one at £49.99
So I can't promise that this is on offer everywhere, it may be a local thing.