Wow, it must have been an old website, the Abel Tasman left about 15 years ago!
Spirit of Tasmania 1 and 2 can be expensive. Travelling in summer high season when you can purchase day tickets is cheaper. CT will cost between $250 and $350 each way. I booked ours in as a small caravan instead of a trailer and saved $90.
If you are a family, look at options of one person travelling on boat, and others getting cheap air fares. If you have freinds in Melb where you can stay and drop your family out to the airport to catch the Launceston morning flight that works well.
You need to stay for more than 10 days to make it worthwhile. Two weeks or more is preferable.
A lot more to see and do than you think.

(Expat Mainlander, still acclimatising to the second head)!