Product & price source checker plugin for wprdpress

We have an ecommerce website built on Wordpress. All of our products are copied and listed from other websites that are not Wordpress.

THis is a backend script/plugin for admin.
The purpose of this task if for you to write a script/plugin that will:
1. check daily if the product is still in stock or not. Admin can turn this script off easily.
2. Check any changes in the price, against the original price when the product was listed.
3. Output the result in the admin product page.

Screeshot: I have attached a screenshot below, you will create a field to display the source URL. With this source URL your script will be able to check if in stock or out of stock

Screenshot: I have attached a screenshot below to show original price. You will create a field to display original price, your script will check source price against this original price.

NOTE: The script must be lightweight and not too heavy on server. Script must be safe from any plugin/theme update.
There is no definite list of website we want to use as our source, so this plugin/script must be able to check on any URL of our choice.