Need custom "Sort By" option for WooCommerce

For a client I need a “Sort By Savings” option for their WooCommerce site. So the sorting would look like this:

  1. Product A (Normal price: 100, Sale price: 50, Savins = 50)
  2. Product B (Normal price: 1.500, Sale price 1.475, Savings = 25)
  3. Product C (Normal Price 15, No sale price, Savings = 0)

Hope this makes sense. The reason would be to show the customer the products they save the most money on, in the top.

Info on the site:
WordPress 5.2.2
WooCommerce 3.7.0
Theme Flatsome 3.8.4
WPML Multilingual CMS
There is both variable and simple products

Looking for price estimate and time frame to start with for client to accept.

Best Regards