Just remember that timber floors, painting, curtains blah blah all cost money so sometimes it can take up to a $100k to finish off a house to 'move in/turnkey'
Ok if you go single storey - I just read above post and not excessive pool then $300k will go pretty far. I'd spend about $250k on a 225sqm house turnkey finished and then some landscaping and pool.
Very doable but I think you need to allow more money for the new house especially if you want to add a pool.
I'd be allowing around $400k to build and up to $100k for landscaping, pool etc
