It could be the when its applying motion blur(if used) or adding the frame to the video file.

I would wait until prices drop even further on solid state drives before buying one, it seems like you are seeking for an answer to get one lol. The prices will come down further in the next 6 months or so and then maybe look at getting one, at the moment they do not offer a great price to Gigabyte ratio at the moment and a normal hard drive will do its job just as well.

You will not see any real benefits in render times by getting an SSD.

Jon

DA Portfolio - http://jonj1611.daportfolio.com/