The cost of building the proposed HumeLink transmission line has blown out by about 30 per cent in real terms, making it Australia’s most expensive power line project at nearly $5 billion in today’s dollars, a NSW parliamentary inquiry heard.

Transgrid CEO Brett Redman told the inquiry – called to explore the costs and benefits of putting the controversial line underground instead of overhead – that the cost of construction and transmission had gone up by about 30 per cent since the original $3.3 billion budget was submitted to the regulator three years ago.