And if you buy the pro version of Quicktime it will turn image sequences into movies. (about 30USD I think)
Super Transcoder will let you transcode those sequences into all sorts of useful movie formats including mobile phones, MP4, DIVX, etc
As for compositing. well :-( The cheapest most Powerful is ImageMagick - if your scripting skills are up to it. Its very simple to use but no big glossy UI.