Facebook Page/Post insights with costs
You can get the Ads Insights using the Facebook Marketing API Insights Edge.There is really many data you can crawl, but unfortunately there is no way to connect them to the posts due to the Facebook ads nature.
If you want to you can try to create ads using Marketing API Ads Managment Edge with data grabbed from your posts and than track these ads.
But there is really no other way.
I don't really understand what you are asking for. Do you want all the costs you had for ads, per specific Page? If that's the case; you can't retrieve that. The costs are provided per ad campaign/set/group, not on Page/Post level.