Hi @alli.braith
That's a really interesting use case.
Currently, I don't think there is a native integration in Amplitude to directly ingest Facebook data via any of its listed Sources. You can read more about them here.
Segment could be a possible solution to achieve this. I haven't done a deep dive into the actual implementation here, but there are Cloud Apps sources for both Facebook Ads and Facebook Lead Ads based on what kind of data you are trying to pull eventually into Amplitude .
I'm assuming some of the marketing spend data you are interested in would live as user properties in Amplitude ? I know they have an Attribution API which might help in some cases.
You can also try building your KPI dashboards outside of Amplitude by bringing together the raw data export from Amplitude and your marketing spend data in a data warehouse.
Hope this helps!