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.
If your revenue is stable or growing you should be able to get at least $20k from the sale, and possibly up to $60k.