If you're at all interested in using a broker, Thomas Smale might be able to help you. I've never used him, but I've met him at a conference and heard him on podcasts, and he seems to know a lot about these things (as that is what his business is about).
He can be reached at his twitter handle @ThomasSmale and his website http://feinternational.com
You could try contacting directly active developers/startups who have released similar apps, they are the ones most likely to be interested (and they're definitely not checking flippa.com). I imagine it wouldn't take too long to find 5 of them and send them an email.
If your revenue is stable or growing you should be able to get at least $20k from the sale, and possibly up to $60k.
You should post it on the Apptopia's Marketplace : https://marketplace.apptopia.com/
Have you considered keeping the app going by putting the funds into an overseas resource?
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Can you pls email me you contact info jtmtrader@bellsouth.net? I'm interested I'm talking to you about the app