Generally speaking if you are planning to spend two weeks in...

Generally speaking if you are planning to spend two weeks in tassie then it would be cheaper to opt for the car/ferry.
However February is our peak period and it can sometimes be difficult to get space for a vehicle, so would suggest you inquire early about your travel plans.
Also keep checking for specials. Things being what they are at the moment you can get some very reasonable deals.
As an aside We have found that when travelling with a larger family it is cheaper for one of us to fly across with the children and for the other to take the ferry with car in tow.

On the bright side of the equation, best place to be in Australia at that time of year!

Happy trades.