Most festivals offer free tickets to Stewards in return for certain number of hours work. The festival website will tell you this.
Most FOLK festivals have singarounds and music sessions, and if it is not a closed festival site these are often free. Or impromptu sessions spring up in nearby pubs.
The festival website will have details of cost, often it is cheaper if you book early.
When you find some that fit your dates do a search for e.g."Whitby festival" and go back 2 or 3 years, you will find all sorts of Mudcat advice about programme, accomodation etc. etc.