I believe you need to change the quality of sound. When it comes to sound for a project like this you can probably take the sample quality down without seeing a huge difference in quality. try using values like and audio bitrate of 22kbps and sample rate of 22kHz. And just because it's an audio sound track with nothing fancy like sound FX tracking from left to right, or front to back, you could probably get away with using audio as mono.
just for fun, try rexporting the video without any audio at all, and see what file size you can get to.
and on a side note you could probably get away with exporting the video at 320x240, but mind you, this is a image quality sensitive video, so I probably wouldn't unless you really want to bring the file size down.
Would you mind posting what codec and compression settings you used? Quicktime has a codec called H.263 which really does a nice job at compressing file sizes down.
*edit* oh and btw, the video is pretty sweet
nice job on the morphing!