Plenty of places on line where you can get highly discounted Group sets.
If racing on a budget-I would suggest Ultegra. Proven to be reliable- fairly light and a lot cheaper than Dure Ace.
With the £ being so poor against the $-Look at this site
http://www.merlincycles.co.uk/Bike+S...+Bike/list.htm
But If speed is the main criteria- Then I would look at wheels and tyres for better performance per $.