Sure it's expensive but I always have a great day there, especially if the sun is shining!
If you want to go on Thursday or Friday, you can get two tickets for £37 by quoting TOP01 when you book. (toptable deal) Not sure if that helps!
Newspapers tend to run offers nearer the time.
To take advantage of this offer simply quote TLEML4 when booking tickets online at www.tastefestivals.com/london or via the ticket hotline on 0871 230 7132
* Ticket offer only valid for Thursday and Friday only, offer closes 1st May 2009. Tickets are limited, booking and transaction fees apply.