You can charge 1000$ but will it be worth it? Can you give x brand that kind of profit? Brands pay you according to the reach and the awareness you can provide to them. And most of the time, the reach mostly stays low in the promotional post. There are some exceptions for sure. If you never charge anyone before, then try around 70-150$. See how your audience responds and what that brand says after that. If it’s a successful one, they will come back for more. And with time, you can increase the pricing accordingly