Influencers princing varies depending on several factors :
their willingness to participate in the project and their appeal to the brand,
their popularity and the size of their community - the bigger the community, the more expensive the influencer,
the average engagement they generate : this reflects the actual number of impressions you will get.
the type of content required: long and/or fix content are more expensive than short and/or temporary content.
To give you an idea, consider $15 per CPM on Instagram and $70 on Youtube.
Lefty provides you with a price estimator for one Instagram post of the influencer. This is available on their Lefty profile page.