You can enjoy a choral Evensong service at Westminster Abbey for free, which combines a traditional mass with a choir.
We went to an Evensong service last week after reading about it on this site, and it was wonderful! What a lovely cathedral, I have never been inside Westminster Abbey before and it was worth going just to see the lovely altar. We will definitely be going back for a full tour, but it was the singing that really impressed us. It soars and sounds absolutely wonderful, and so holy. What an experience.