I have been looking into the possibility of travelling to Tassie with my caravan and have been given a better quote from this web site.
http://travelwithacause.com.au/
Now I am not saying that their prices are cheep but they are better than the Spirit's prices. Their price was around $120 cheaper return. I couldn't get the CMCA discount with them though.
The new Liberal government may offer something in the near future to encourage more tourists.