This is a perennial problem for choirs, never more so than in these times when choral singing is popular but audiences may have watch their outlay.
My comments here are really about the Bath choral scene, which I know about both as audience member and performer. Many audience members seem to be very loyal to one particular choir, attending their concerts rather than others. One such person could easily be worth £100 a year to a choir, if they come to all the concerts and bring another audience member with them each time. If choirs can create such relationships and work on them, the effort of fund-raising would be significantly reduced.
And yet I don’t see much effort put into building these relationships, beyond setting up a mailing list here and there. For example, if choir members mix with audiences in the interval, they could look out for people they recognise and chat to them. It was one choir’s failure to do this that caused me to leave one of their concerts and not go back to any further ones. It’s such a simple thing to get right.
An obvious constituency to target is people who once sang in the choir, but now don’t, together with people who have expressed an interest in joining but don’t as yet sing with the choir. There are ways of wooing such people, for example by having a larger-scale concert and inviting some of them to take part, as Bath Camerata used to do on Good Friday. They will then be more likely to come to other concerts. Another very simple thing to get right is dealing with those who ask for auditions; a waiting list for auditions should be just that and lead to an audition. Probably the Paragon Singers have lost several hundred pounds over the years because I’ve not been inclined to go to one of their concerts while I’m still on such a list!