Theatre prices and booking /transaction charges

I was just looking to book a theatre trip and am puzzled. Why do you have to pay a booking fee of £1.99 for a less popular show and £3.99 for a musical? Surely the process is exactly the same. I am sure the booking charge used to be £1 for all but that may have been long ago! I was horrified at the prices of seats these days. I like to treat my granddaughter to a matinee performance but the theatre plus lunch plus an ice-cream or drink makes it an expensive outing. This is not in London but our local theatre. I wanted to see ‘Pretty Woman’ but upper circle seats cost £71!