Here's the response from Zenfolio - nice that you can contact them directly and they respond quickly.
Thank you for your interest in Zenfolio and for bogging about us.
We do have a Premium plan in the works that will allow you to set custom prices, assign watermarks, and remove Zenfolio branding, among other things. We do not have a date to give out when this will be available, but it is something we had in mind all along so it will not take longer than a month or two.
Let us know if you have any other questions, we are here to help.
Zenfolio Customer Support