Help needed with iOS apps

Hi everyone, I'm working for a real estate company at the moment and they are looking to get an app running on the android platform that we can use at our open homes. There is one on the play store called Open Home Register, but its crap, I paid for it and it doesn't work that well.

There is also one on iOS called OpenHome Pro, I've been in contact with the dev, and at the moment they have no plans to release an android version.

So, my question is, if I got permission, whats the work involved porting the app, or even rewriting to work on the android system, both tablet and phone? On average how much would we be spending on a dev to help us with that?

If somebody could help me that world be great.

Also I should mention that I have permission to work on the Open Home Register app, but the way its working just doesn't make things easier for us, so I thought start again using OpenHome Pro as our base because its a much better app.

Thanks in advance guys/girls,
Evil.