Add functionality to existing iOS app (iPhone / iPad)

Hi, I have an existing app that works but I need to get a few things added. It is a quiz app where the user is shown a picture and then questions about it on the next screen. - Need to apply better UX (it has about 6-7 screens in total) -- If you create one from scratch, OR -- If I create one and send you mock-ups - Ad and in app purchase to remove ad - Game Center -- Leaderboards (view, post scores), and -- The ability to play multiplayer games - Changing from arrays used in the code to use an SQLite database instead. It'll have to be encrypted (maybe use SQLCipher) - Fixing an issue with background music. It currently creates a new AVAudioPlayer each time the main view appears even if music is already playing which results in more and more AVAudioPlayer objects being created and played simultaneously. *** Please quote how much you would charge for each requirement individually or your bid may not be considered *** I am an iOS developer as well but because of lack of time I am no longer able to work on my apps. As such, I am looking for someone who can work on my apps for me **at a reasonable price** and I would like to work with them for my future projects as well. VERY IMPORTANT: Please do not post stupid and unreasonable bids. I know how much work goes into each requirement and the primary purpose of this posting is to gauge who charges fair prices and work with them on future projects as well. Thanks.