Tasmania Car Rental / General Advice

Start with the consolidator, then go direct to the car hire place it spits out as the best deal, and you will almost certainly get the same deal, but with the certainty of booking direct. But you can still get better deals through airline frequent flyer programs, and by being a member of a motoring club.
Avoid Europcar.

Lo-Cost Auto Rent is a reputable agency in Hobart that I have recommended to friends and a few people on the forum over the years, with good success. Their cars are slightly older (5-6 years) and I think you will find it considerably cheaper than the large firms (Budget / Avis / Hertz etc).
A couple of other reputable Tasmanian companies that you might include in your research are Bargain Car Rentals and Rent For Less (they all have websites).
It is important to make sure that you are allowed to drive the car on unsealed / gravel roads.

Here is a good thread from a couple of years ago from an American guy who hired a car and travelled around Tasmania for a couple of weeks staying in budget accommodation:
https://www.lonelyplanet.com/thorntree/forums/australasia-pacific-australia-new-zealand-antarctica/topics/tasmania-thinking-of-a-visit-at-end-of-november-early-december?page=1

Last time I was in Tassie I used Hertz and was happy with the experience but you are paying higher rate than some providers.

If you are in Hobart on a Saturday then visiting Salamanca Market is recommended.

The best thing about Tassie is its natural environment. The Huon Valley, Freycinet and Cradle Mountain are high on my list of recommendations. It also has some great lakes like, well, Great Lake, Lake St Clair and Dove Lake. While the east coast is great it is probably not the best time to be on the beach but if the weather is good enough places like Bicheno and St Helen's are lovely. It gets cold (well, cold in Oz terms) in Tassie, be prepared.

We rented a van around that time of year a couple of years ago from Tassie Motor Shacks near Hobart airport and it suited the purpose. As budget travellers we pretty much stayed in the van in a mix of free/paid camp sites. Maria Island was great and I was recommended Bruny Island but didn't get there this time.

Wow! So much good info so soon. Thanks.
A few more questions:
--Do I want a car I can take on unsealed roads? n the past I've gotten a rental not allowed but might but took an unsealed road for a few clicks once in a while if the road didn't look bad. If I did rent one allowed on unsealed roads would it be that much more expensive? I normally use the insurance on my credit card so I might also have to take a local insurance as well upping the cost.
--I'll be in Tasmania 22 April to 6 May. I only have accomodations for Hobart from where I arrive and depart. Given the lower tourist season can I pretty much wing it with the rest of the time, just getting accomodation as I need it? And especially since I do not have an itinerary and like to be spontaneous. I'm wondering if despite it not being normal high season there could still be a lot of locals since the AUD is down. (This time I'm lucky coming with USD)
--Can someone recommend a good SIM card. I'll spend only a couple of days in Melborne and most of myntime in Tasmania.
Thanks again.

If you're just visiting the major tourist spots, unsealed roads shouldn't be a problem. Cradle Mountain, Strahan, Port Arthur etc - perhaps some small minor roads unless you're planning to do something like the Highlands lake road or Arthur Rover. 2WD should be fine.
Most people try to do Tasmania in a week, which will let you have a great holiday but not the whole state. 14 days will give you plenty of time to do both coasts and see Cradle Mountain, Freycinet, Port Arthur etc and some of the lesser, more outer spots like Stanley, head down the Huon Peninsula, maybe head over to Bruny Island, spend a few days in Hobart (and, as mentioned, time this for a Saturday for the Salamanca Market, which is worth the effort)
You will have no trouble finding accommodation. This is not peak season, Easter is gone, and school holidays end that first weekend. Maybe cradle mountain would be worth booking, but otherwise just turn up.
SIM cards are not regional here. We have 3 major national phone companies - Telstra, Optus and Vodafone, and others who resell their service. Telstra is generally a better bet in more remote areas, but all 3 have decent national coverage. Go with the cheapest.

Thanks harry_ramsden.
Outstanding advice!
Much appreciated.
So, to make sure I got you right. I can do without renting a vehicle allowed to go off sealed roads?
Nice to have but I can easily live without one?

We went to the Stumpys Bay camp site in the Nth East no problems and although it was clear enough road it was unsealed as I recall. Also we spent 11 days and didn't see the west coast or Bruny so it depends how much you squeeze in as to whether you will end up seeing east and west coast. The furthest west for us was between Cradle Mt and Queenstown.

You can easily get the most out of Tassie by staying on sealed roads.