On campaigns, the price of the average hero-rank poster is from $50 to $100 but if it's all about you, you should be the one to set the price, and it depends on how confident you are in delivering visibility for your potential clients' platform.
Your reputation and other services that you have like if you have a Twitter account with over 5000 followers you can include that, you offer the price and the client will take it based on their needs and what they are looking for a promoter.