Wings is a free 3d modeller (and can do a lot of what the very costly high-end apps can do, albeit in it's own style).

See the Wings forum here at 'rosity to get a link for the download..
You could also ask in that forum for advice on how to create stalactites etc. They love to help ('cos it allows them to show off.. - but don't tell them I said that..)

Cheers,
Diolma