finyo, also be prepared that the answers from them may be much the same if you received here. If I called a local US homebuilder and asked how much it would cost to build a house, I'm quite sure they wouldn't just throw a number out on the table. I wouldn't expect them to. As many here have said repeatedly, there are a number of variables to be taken into account.

Well balancing out material and costs labour costs is one thing but 2 story is quite a bit cheaper to build ; far less foundation and roofing area. It also simplifies the plumbing and of course is far more energy effective as downstairs heating will also contribute to upstairs heating. PROs can develop on this. And as Curt points out, modular is a very fast and cost effective solution which can allow you to put your pennies into better quality. Be very careful to select a known and competent professional if you go this way though, i don't know about NZ but europe abounds with cowboys ; low costers are to be strictly avoided.

When installing over top of old ceramic/porcelain be aware that you will most likely have to "sink" the old tiles in cement to do this. That means grinding down the tiles a little (rough up the surface) then the self leveling cement is poured and allowed to dry. The new floor is then laid over top. Vinyl is notorious for requiring EXTREMELY flat surface. A ceramic tile rarely has this requirement (grout lines and "high spots" around tile corners give problems). A glue in place tile is also going to have the same problems and the same solution = sinking the tiles in cement. This adds extra costs to the floor. A rigid floor like a cork floating floor can handle a bit more floor deflection than vinyl or laminate planks. If labour in your area is relatively cheap...you could probably have the tile removed and the sanding of the mortar done for the same price as coating in concrete. You will also have the luxury of being able to lay any floor you want once it is done AND you don't have to worry about increasing the floor height. It is possible to sink the ceramic in cement...but is it the most cost effective option? Maybe not.

Bottom line, a toe kick is to stop you stubbing your toe and get your closer to your worktop counter. If you can fit your foot underneath it in shoes or barefoot while standing at a counter and not stub your toe or hurt your upper foot, you can do it. If you cannot, you will be forced to stand back further at your counter and that will not be comfortable for you in the long run.