cost us about 6k for the 41 thou that's with upgrades to the bathrooms upstairs.
It will depend on the size/type of tile you are using downstairs and such things as water sealant, colour grouting. Remember, the large tiles need extra for laying time and may impact on the height the first step needs to be. See Michael (the bald one, there' 2) at Don's Tiles and he will help you. He seems pretty clued up, if a little slow at getting samples...
EDIT: this cost was not inclusive of the media, lounge, study, as we had those with carpet...