At the time of writing Website Clone costs $1.50 / €1.15 / £0.98 per clone, inclusive of 100MB.

All additional data transfer after the first 100MB is charged at $0.003/MB.

There is no recurring subscription fee for website clone functionality - once you have either a WorpDrive, or an iControlWP subscription you may use the website clone feature as often as you like, and only pay when you use it.