Audio Download App Designer

We are looking to find an individual who can design applications for future web and mobile platforms. Briefly, it is our intention to sell audio downloads (music in mp3 etc.) throughout the world. 1) We need to know costs for designing these apps and integrating them into our Word Press based web pages for download. 2) We would like to find an expert in this industry who can advise about current "best practices" and methodologies in this niche industry. For example, how would we get our song(s) into the itunes platform - what would be the cost? How much are individual songs being purchased for these days on the net? We are only the design phase of what we believe could be a large business, but we currently lack this key knowledge. If you have any specific experience in this industry of audio downloads including building apps, seting up platforms and maintenance of such, please send detailed summary of experience along with a budget for these concepts broken down in the manner you see most fitting. Regards