You're in the same boat as a lot of other iPhone app marketing--spend more than you take in, hope you make it up somewhere. The problem is, there are a lot of much better ways to throw away app licenses:
* Giving promo codes to bloggers, who are definitely influencers and costs me nothing for the first 50.
* Just gift apps to people myself, which is 25% cheaper, and I have direct control over who the people are, so I have firsthand experience that they're movers & shakers
So really you're going to have to convince me: first, that giving away licenses is a good idea and second, that paying you to give away licenses is better than doing it myself. This means you're going to need really stellar users who are better evangelizers than my friends & family, who care about the product mostly because they care about me.
That's going to be an uphill battle, to say the least.
One thing that might help you is a couple of testimonials or success stories from other developers. Find a "deadpool" app that really does show some promise. Reach out to the developer and offer to promote it for free in exchange for access to all the sales figures. If you can demonstrate "hey, we made this guy 10% more than we would have charged him" that at least sounds promising enough for me to give you fifty bucks and see how it goes.