Based on the most popular festival locations in Europe (apart from Britain), I looked up the cheapest travel options for each location.
If you are travelling in a group in Germany, there is the option of a group discount, click here for more information.
If you are travelling in Belgium there is the Go Pass 1 which is only 6 euros for one single journey anywhere in the country for people under the age of 26.
Budapest is infamously a very cheap place to holiday in and the public transport is no exception. For what is the equivalent of 95 pence, you can get one single travel ticket on bus, train or metro.
In Portugal, if you book your train travel between 5 and 60 days in advance, you are entitled to a 40% discount
In Denmark you can travel on any public transport -unlimited- for 24 hours for just £8