The festival runs from 22 August to 29 August but the key event (i.e. when things get rather messy!) is on the final day.
A quick web search found this link to a tour operator:
http://www.topdecktours.co.uk/content.asp?Docu ment_ID=35961
The tour price of �135 includes 2 nights hotel accommodation plus travel to the festival and local tours. You have to make your own way to Valencia. The Valencia airport website states that the following operators have direct flights from the UK to Valencia:
Thomsonfly (from Coventry)
Iberia (from Heathrow)
easyJet (from Gatwick & Stansted)
Ryanair (from Stansted)
The airport is only 8km from the city centre. A taxi would cost about �14 but there is a frequent bus service for about �2.50.
Chris