CPI goes from 0.50 $ up to 2$. However, there are several factors that need to be considered, in particular:
A) Type of App:
Some apps can pinpoint the competitive advantage that Facebook Advertising possess, such as a great audience targeting or precise interest targeting (dating, gambling, classified, e-commerce)
B) Budget:
Facebook is the biggest publisher and users spend on this app up to 18% of the total time spent on Mobile. However, the more you want to spend, the more different campaigns you need to carry out to keep the performance at a good level. If you want to spend 2000$ a day with the same banner, targeting the same audience, your CPI will rise day by day.
C)Measurement:
Facebook shows both post-click and post-impression installs, as an indirect effect of their branding advertising. Normal display networks show only post-click installs and measure the CPI based on that. Therefore, Facebook CPI is lower (discrepancy between post-click and post-impression is normally around 10%).

Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath