Before/After Audio Player

Here is my situation: I need a Before/After Audio Player. An exact example of player is here: [login to view URL] under FEATURED ARTIST SAMPLES I need the script to be done and saved in SwishMax 3 so that I may change the audio files and buttons in the future myself. Some rough buttons and audio are attached. I am thinking two audio files are streamed at the same time and the Before and After buttons switch/mute the volume between the two tracks while the timeline is maintained (this is critical). The files should be referenced rather than embedded to keep the file light. Please give me the cost & timeline estimates. if you have done some work on the similar lines thats added advantage. Thank you