Re: Never happen here.
The high cost of HS2 is primarily because it's had to swallow up the costs of rebuilding Euston. (Network Rail were about to green-light a rebuild to their own design around the time HS2 was announced. Network Rail then realised they could get HS2 Ltd. to pay for their grand plan.)
It has also been forced to put lots more of the line into tunnels to appease the usual NIMBYs and BANANAs along the route.
In fairness, the Channel Tunnel isn't all that much shorter and is still working today. It also took rather less than 17 years to build, though the high-speed link (today's HS1) took substantially longer to design, build and open.