Why there is no single rate
The price of a sponsored post depends on several variables: the size of your audience, but above all your real engagement rate, the format requested (dedicated video, integration, series), the usage rights you grant the brand, any exclusivity, and the turnaround. Two creators with identical follower counts can legitimately charge very different amounts.
Be wary of ready-made grids that price you purely by follower count: they ignore engagement, which is usually the real signal of value to a brand. A smaller but highly engaged audience is sometimes worth more than a large passive one.