The 20-30% fee is not exorbitant. Many agencies charge a 5-10 pound
surcharge on top of a fee. When you choose your hotel, you might ask the
management if they can obtain excellent tickets for you - and inquire what
their fee would be. Another alternative to consider, once you are there, it
to check with the half price stand, which sells tickets for the same day (you
can find this location through any extensive London web site or good tourism
book). Harrods (the department store) also has an agency inside, and can
often find a good ticket, but you will pay the above commission. And, the
Theater's box office, often finds itself with tickets that have not been
picked up, or been canceled at the last minute, and is worth the phone call
or to stop by, while you are out doing sight seeing or shopping.
Just some alternatives that you might consider, but do try http://www.playbill.com.
Roy &Wanda Faires