Canada

Bipole III transmission line, built to deliver power from northern to southern Manitoba, jumped in cost from $2.2 billion in 2007 to over $5 billion once completed roughly 10 years later.

No mountains and cheap land rights. This was also a project that was backup/resilience focused, just as any new Canada trade project would be. A 5% ROI (yield), at 10% capacity utilization (36 days of backup per year), excluding all maintenance and operations costs for 2gw transmission line would require $3.42/mwh cost which doesn't seem that bad, but hydro capacity is almost always under 50%, and there was just one main incident that resulted in a 4 day power outage in last 30 years. So putting cost as at least $10/mwh or even $20/mwh is reasonable. Main value is job creation boondoggle.

Much higher resilience value for Hydro power (subject to droughts impact on capacity from global warming) is solar and batteries and EVs with V2G. 5gw solar (can cost under $5B) will provide 5000 mwh (equivalent to 10% capacity on 2gw hvdc line) on the worst winter day, 15000mwh on average winter day, and 45000mwh on typical summer day. V2G is generally a consumer expense, but paying them $20-$50/mwh margin for arbitrage ensures full solar sales, and lets individual consumers have 4+ days of resilience if they want to prioritize that over V2G profits in emergency. Consumer solar is also a private expense that lets them arbitrage EV power to greater profit. Even if all equipment/EVs is China sourced, there is significant local job creation/expenses for cheaper power and power resilience.