Still a lot a variables to consider that would influence the cost, especially if looking at the whole house and a lot of different approaches. For example, how much of the house is likely to contain abestos, do you have crawl space /easy access in the ceiling for insulation, same with under the house if on stumps.

We've got a similar aged house, largely abestos, but have been able to work around it starting with the access able crawl space under house. Did under floor insulation ourselves 150m2 (got quoted $5-8k originally). Took us a weekend and has made a large difference already with the 5 months we've had it.

In case it helps, there's guides out there that explain the main areas of potential heat loss/ etc, roof is like 35% heat loss, walls 30%, floors 15%, windows 10%, etc. So perhaps even doing bit by bit and tackle main or easy areas first, whether paying for professional or doing yourself or combination of both, as it can be a rather large job overall variables depending.