EdC, thanks for your explanation.
Winter days in the Barossa are a little colder than near the coast, generally 10 - 15 deg C (48 - 56F I think), nights are often 2 - 7 C (35 - 43F) but sometimes up to -10C (too hard to convert!).
Wood is sold here by the trailer load (imprecise) or by the tonne.
I presume a cord of hardwood might be about a tonne (2400Lbs)?
We have a wood stove in our house as many around here do, but we use our own old vine stumps (soft) or broken vineyard trellis posts which were always hardwood in the past.
Currently we use creosote treated softwood trellis posts and these, I'm told are unsafe to burn and environmentally unfriendly. So we're cutting down on the use of the treated softwood by going one wood post then two 1 1/4" 304Stainless tube posts and so on. We've used galv steel posts but these rust off at ground level too quickly, but Stainless is getting mighty expensive.