My understanding is that underfloor heating is better suited for northern hemisphere areas where it is freezing cold for days or months on end.
Or Invercargill/ Dunedin area :) I spent a long time determining whether it was worth it for a new build I am working on at the moment. The cost to install was going to work out at about 60k with a totally automated system off water heating heatpumps. Instead decided to go with a multiunit heat pump running off a large single compressor, so you don't get ugly boxes all round the house. Also going for wood burners as well. This means you get heat when you want it without having to plan. Also get cooling for summer. It was also supposedly going to cost over $20 per day to run the underfloor heating system. Then there were also maintenance charges for flashing out the tubes etc. But I would look at underfloor heating if I was to do a small house, and was doing alot of the install myself. It just didn't work out on a large house.
What part of Otago/Southland are you in @mattwnz? About to build in Mosgiel, and a Hydronic UFH system is less than $20k (including the heating of all domestic HW).
Mine was in the wellington region but was estimated 60k +. But we rarely have winter days that are cold 24 hours of the day with no sun, and on sunny days, can use passive solar gains with large glass windows/doors to heat the tiled slab.