Yes. I did changed my gynae halfway. The first one I went was very expensive, far more than yours. But she was very experienced and we were trying to have a baby, after many tries with other gynae and methods.
I told her that her consultation was expensive and wanted to change to another gynae. She was opened about it and told me that I can change upon 20 weeks when my baby was more stable.
Anyway, the gynae package at most clinics starts from 4 months of your pregnancy.
If you do not want to tell your current gynae, then you tell the nurse or counter that you are going for another gynae and dont wish to make anymore appointment.
Hope this helps.