Hi there, I updated the blog I wrote last week which showed how to make a cheap ($50) wireless fpv monitor. This week, I updated to show how to add droidplanner to this setup, and for me it cost zero extra cost. Should cost you about a dollar to make if you're inventive. (Total cost $51)
Update is at the bottom of the blog article. I'd be glad to hear of anyone who decides to build this for themselves.
Article here: http://dalybulge.blogspot.co.uk/
Happy flying :)