There are two ways to create a promotional price for your product.
You can create a separate Price List for the items you wish set a promotional price for and then add the promotional price via the Inventory section
You can create a composite variant of the product you want to add a promotional price to and then add a price to that composite variant.
Tracking Items Sold Under The Promotional Price
If you would like to create a promotional price for your item but wish to track the items you have sold with the promotional price, creating a composite variant would be the way to do it.
Essentially, the image below shows what your composite variant would look like.
You then have the flexibility to go ahead and key in your promotional pricing in the details segment of the composite variant.
Thus, when the Composite, Cat Promo, is sold, the stock for Cat will also be updated. You can easily differentiate those sold under the promotional pricing as they are two different variants. Search for Cat Promo when you want to find out the number of items sold under the promotional price. You can also generate a Sales Order Report for a better overview.