Seeker, many of the grant-funded theatres run youth theatres and have education outreach programmes - and can be contracted to provide an out of schools programme for the cost of a tutor. Do you have a non-commercial theatre in your area?
DS's school works with FilmClub and an outfit that runs the rock band classes (though I'm not sure who it is that does it). We therefore pay £30 per term for rock band, while the vast majority of extra-curricular activities are free.
Not drama or choir, but StreetGames are a fantastic national sport project that work in partnership with schools, offering sport and training / volunteering projects for young people as an extra-curricular activity, and have a branch in Kent here.