Blender is free, but I struggled to get it to do anything sensible... After an hour or so, I gave up and went back to Google Sketchup
having some ideas just now i am struggling with blender too. its completely messed up imho in terms of workflow and logic.. just like late lightwave, which i might fall back to, even though i liked the similarity of the interface and blender being open source.
sketchup doesnt sport particle anim, i assume, it probably barely even has a renderer, does it?