I came across two websites recently that have calculators that help you determine an appropriate rate to pay a social media influencer based on the number of followers they have and their engagement. I have no idea how valid this information is but I hadn't seen anything like it and wanted to remember these links in case I'm ever trying to determine this type of information.
I haven't looked into either very much, but I assume that you have to take what their automatic calculators determine with a grain of salt. The relevancy of those followers are very important in determining what that influencer's post is worth to you in particular. There's also a huge variable in what each influencer would offer like how many posts, tweets, etc does the rate include. Does it include photography? A permanent blog post on their site? A pinned post? etc.
That's just my disclaimer to remind you that no automatic software can exclusively determine market value – but they can provide a reference to help you determine it. What other tools out there exist for this purpose? Drop a comment and let me know.