I don't know what it would cost for your drain replacement. That's something that has to be seen first hand. Call a plumber for a quote. They will not likely know what a Kerdi drain is, so try to have that info for them when they show up for the estimate.

Go thru some of the articles on the web site for tutorials on proper shower construction IE: mud beds,waterproofing etc.

Its also best if you keep this project in a separate thread. That way it will be much easier for everyone to follow your project.