If this is actually true you should be doing affiliate installs which routinely pay out $1 with no (or high) caps. You could literally make tens of thousands of dollars daily.
For example, with less than 50 €, the ad has already been seen by around 15 % of the total audience. No matter how much we throw in, it's going to be going slower and slower from now on. But it is enough for us to get seeded among a few hundred medical professionals, and then rely on word of mouth to carry us forward.
Edit: It's also a free app, just to make that clear.
This is just good marketing advice for smaller businesses. Find as specific a niche as possible and market to that. Maybe the parent's product serves a very general audience which may make it harder to market.
http://bigosaur.com/blog/28-facebook-ads-android-players
You need to use the targeting options, otherwise you're wasting money.