I'll be better able to advise on the cost comparison of newbuild versus relocated once we're finished and a bigger home may be more worth moving than a smaller one to get a saving, as adding an extra room later may cost about an extra $30K or so, whereas getting a 4-bed transported shouldn't cost $30K more than a 3-bed one, if that makes sense!
I understand what you mean and shouldn't be an extra $30K just to move a house with an extra bedroom. The only problem I have with relocating old houses is the difficulty in meeting the standard of a newly built house. (this is not to say you can't). Speaking from experience (and i'm roughly speaking), the cost factor it takes to renovate existing houses is like 80% of the cost of to build a brand new house. Just look at a leaky syndrome house where the external cladding has to be replaced - (as much as 80% of the cost of the whole house). I'm not trying to say relocating a house is a bad thing, it's just that to a person that wants the comfort of today's newly built home will pay a lot to retrofit an old dwelling to that standard. Come to think of it, when I look at issues like double glazing, insulation (roof/wall/floor), it's hard for me see any savings compared to building new. But by all means, if you want that old character house look - there's no reason why someone can pay more for it.
Ralf may be able to add some thought but from what I gather, an insulated concrete slab floor (with ie 50mm polystyrene on slab and around perimeter) has more insulation value than a house on piles (where air flows freely under the floor boards).