Not sure about licensed stores but at corporate stores it’s a 50-75¢ upcharge. Adding vanilla bean powder or berry scoops or something always has an upcharge, unless it’s already in the drink. So you could get a Strawberry Açaí with extra strawberry inclusions for the same price as the regular drink, but you can’t get a Strawberry Creme Frappuccino with strawberry inclusions without an upcharge

If it’s included in the drinks then any extra doesn’t get charged. Like mocha sauce is already in the mocha frap so if customers want mocha drizzle on top, they don’t get charged extra. Also, idk if this still applies but things of the same consistency won’t add extra. So if you’re getting a vanilla latte with a bunch of other syrups, it’s just 0.50 for syrups in general. But you can add white mocha to a mocha without extra charge bc the sauces are the same consistency (sauce) (this needs to be fact checked tho. It used to be true)

Licensed stores have a long list of policies they have to follow and what they can and can't do for pricing. It's all in the contract that let's them open their licensed store.

Some of the add ons are obvious because it uses more product and costs the store more money to make the drink, but there's no consistency, and it often annoys customers who don't know the difference between licensed and corporate stores.