If it's Gran Turismo you want, remember that the one available at the moment is effectively a demo version. You only get six tracks and a selection of the cars available. The "full" version of the game was slated for release in early 2009 last time I checked so it might be worth waiting until then as the prices should've dropped a bit.
To get the best price now, check out
http://www.pricerunner.co.uk or
http://www.dealtime.co.uk I've both of those sites pretty reliable for sourcing the lowest internet prices, alternatively if you're looking to upgrade your mobile phone in the near future, look at the phone adverts in the back pages of The Sun - you can often get a free PS3 chucked in with a new contract - that's how I got my Wii.
In terms of HDD size, the only one I've seen for sale recently is the 40GB one, the 60GB is not available for general sale anymore and is going for silly money on eBay. The 40GB console is not backwards compatible with any PS2 games either. The standard pack only comes with one controller and no Ethernet cable, but it has wireless capability so that's usually a moot point.