Changing price after x units sold. Cant find anything! Help me :)

Hello guys, I run a fresh produce delivery business, i am looking for a app that allows me to automatically change a price after units sold, everything seems to be date sold. Example:

I buy 100 Pineapples at a good price, I want to set the next 100 pineapples at XYZ price and after they have sold out, revert back to my old sell price. This app/functionality would be a game changer for me.

Do you guys know any apps that offer this, or 3rd part back end software that i can control prices from?

Thanks a bunch!

So it’s like automatically updating your price based on inventory level?