(this post is a feed post from my comments on reddit)
r/Entrepreneur
I worked in affiliate for years (basically CPA-paid marketing)
to address the question you’re asking you actually needs to ‘zoom-out’ to a business strategy level to resolve.
you need to create a financial operating model that allows you to see the conversion funnel – eg. Impressions > clicks > Leads (MQLs) > sales calls > signed contracts
you want to then have the average order value of the signed contracts as well, segmented by advertising channel. and you also want to allocated marketing budget segmented by marketing channel.
now that you have this, you can calculate the ROAS for each channel, as well as the comparable cost per – impressions (CPM); clicks (CPC), Leads (CPL/A); sales call; signed contract.
then you can compare the channels based on relative volume as well as performance.
this is in very simple terms what i did for most of my career in media buying, think of it like allocating investment into different stocks, with each stock representing a marketing channel, and figuring out a return.