You need to consider implementing an SDK for tracking installs i.e appsflyer, adjust etc - then you make it available to ad networks and you pay them per CPI ( Cost per Install).
You can set restrictions too what is considered an install etc by setting no-incent traffic, these geo's etc.
Then you publish on the app stores and track (since SDK is within), what was from your ad campaigns, or via the networks, organic or not and so on.
You can get the CPI costs quite low depending on GEO's too.