Kovacevich/Argerich, Wigmore Hall: entry level £17, highest £62
Barber of Seveille, Opera North: entry level £15, highest £68
Cav & Pag, Royal Opera: entry level £13, highest £250
The Passacaglia Test rather blows out of the water the misconception that concert and opera tickets are expensive! A thorough and well-researched article, well worth reading.