override opencart pricing and quantities with custom table.

We have added a table called "clearance" to our database. In that table are 3 columns "product_id, "quantity" and "price". The logic is, when the quantity is >0 in the clearance table, we want the clearance price to be shown for the product as a special/on sale. The site should also display text under the "add to cart" button saying "Only X items left in stock at this price". The price in the clearance table should also be imported into our google shopping feed, if the the quantity is >0. When the quantity is <= 0 in the clearance table, the regular price and opencart behavior should resume (the clearance table is disregarded). When the job is done, I will need time to test and make sure everything functions properly. All changes should be documented in a txt and sent to me when the job is completed.