I would take a look at inmobi

Is it on a downward trend? What are the ongoing costs? This will help determine a break even price.

What skills do you have?

Use a combination of mobile network ads, Facebook ads and keyword changes in your app to help discovery . You want to give your app a push up the higher rankings and let iTunes take care of the rest, once you are up there. If you get up there and downloads drop when you stop advertising, something needs to change in your app to make it sticky. Let's hop on a call for more in depth action steps.

20-100k/day depending on their size - it's a big investment. Why don't we hop on a call to discuss further and next steps to help you target them?

Your app should include a login that would validate with your servers who is/isn't an active member. Let's hop on a quick call and we can discuss specifics.

free services can be great to get them into your funnel. If they don't understand the value, I would create online seminars or videos that you can point them to, to educate them. Let's hop on a call and discuss a gameplay for you.

I've targeted the legal niche with great success through a combination of outbound sales and Facebook marketing. Why don't we chat about Facebook as that was where my greatest ROI was?

I agree, that offer won't work because of the incredibly low payout, especially on a b2b offer. If you had a better paying offer, you would need to track your ads and see which is converting best. If you would like more help feel free to give me a call

You need to check your analytics and see where your visitors are leaving. Also test your sales copy and modify it until you see results. Give me a call if you would like some in depth help.