Ubercart- free shipping through pay per click
You need to use Commerce Free Shipping module.


  This module provide a solution to add Free shipping rate on top of
  commerce_shipping services.
  
  This module change the price of the service to 0 and can display a
  message to the user saying the free shipping are applyed or the amount
  left to obtain free shipping.
  
  You can use this module to have a free shipping rate by:
  
  
  Shipping service
  Total amount of the line items in the cart (don't take in account the shipping line items)
  


How to setup free shipping