@Connor $25m/km if you can do it predominantly at-grade; there are examples in France, and I think also in Germany if you net out the tunnels, not to mention Spain. But a lot of places like els, esp. in Asia, so you get higher costs, in the $40-50m/km range, like the Beijing-Shanghai HSR (IIRC low 50s in today's money?) or Texas Central. India is even more expensive because cultural cringe costs money.
@Connor $25m/km if you can do it predominantly at-grade; there are examples in France, and I think also in Germany if you net out the tunnels, not to mention Spain. But a lot of places like els, esp. in Asia, so you get higher costs, in the $40-50m/km range, like the Beijing-Shanghai HSR (IIRC low 50s in today's money?) or Texas Central. India is even more expensive because cultural cringe costs money.