Hi

Let´s not talk of high quality, for the following reasons:
_ if you want your house with 3m headroom instead of 2.6
_ if you want to cover the walls with massive wood
_ if want doors larger, higher and with larger thickness than normal
_ if you want very expensive materials in the w.c. and kitchen
then the costs will be very diferent.

Let`s consider a good quality house, unifamiliar(not geminate), with ground floor and first floor, with:
_central heating
_central aspiration
_double window glass
_electrical rolling shutter
_garage electric gate
_telecomunications board(4 tel operators+internet+tv cable+sat+normal tv)

Assuming you already have the ground plot ,the project and licences, you go to your bank and for this kind of a house they normally will finance you between 500 and 600 Euros/m2, but they do not finance tax(iva-21%), wich means your cost will be 605/726 E/m2 and this is without garden,fences and frames.

As you can see the prices of the plots are responsible for the diferent prices you have in the markrt

Best regards

Luis