Create Server Code to Watermark MP3s and Then Identify Mark

We need to create a script or set of scripts that can apply a unique audio watermark to a MP3 on the fly and then also a tool for identifying the watermark in an audio file. The typical scenario would be that a person come to a website that host a MP3, put in their email address, and a MP3 file sitting on the server is then watermarked with a unique audio signature to identify that person's email address. The person then downloads or streams the file. Later, we would be able to take that file, run it through some kind of processing script or tool, and it would tell us the unique ID embeded in the file based on the audio signature. The watermarking tool has to be something that can run on a web server (PHP, Javascript, FLash, etc) but the extraction tool can be a desktop client if that is easier. Willing to pay up to $500 for a fully functioning set of scripts and tool that does all of the things described above to our satisfaction. Thanks, Scott