What are the ratio between the 30 minute and the 1 hour reading being booked? Is it mostly 30 minutes with a few 1 hour booking, or is it more balanced?
I was going to suggest that if it's balanced, then maybe keep the price the same for the 30 minutes, and increase the 1 hour reading prices? I'd guess those who book 1 hour reading are less price-sensitive then those who book 30 minute reading.
I guess that depends on how much extra time outside of the reading is spent on preparing for the individual reading per client.