You can set a preferential price per minute for your customers by going into your account at Setting ⇒ Price.

There, you have two options:

a. Add the member manually by using the Skype ID he has connected to his account (blue arrow in the screenshot)

b. Search the member in the list (manually, or by using the Skype ID / red square in the screenshot)

You can set the preferential price by editing it in the "Set Price per minute" box.

Now, each time you have a pay-per-minute show with that member, this price will be charged instead of your general price per minute.