Yes, however the cost of a viaduct is largely dependent on the height required. The Alasca pipeline came in around 1.2 million per mile dispite vary harsh conditions but it was also rather low to the ground.

Maybe I'm confused about the meaning of the word "viaduct", does a pipeline count as one?

A pipeline doesn't need viaducts because it doesn't have severe restrictions on curves. It can follow terrain:

https://en.wikipedia.org/wiki/File:Trans-Alaska_Pipeline_Sys...

A high-speed railway needs to be flat, so it needs tall pylons to support it above uneven terrain:

https://en.wikipedia.org/wiki/File:SNCF_TGV_Duplex_Viaduc_de...

https://en.wikipedia.org/wiki/File:Millau_Viaduct_constructi...

Trains often need viaducts due to those restrictions but a multi span footbridge over a swamp is a viaduct as is the Disney monorail. My point is simply elevating a span is not that expencive. However, as you say high speed rail needs a vary flat track so cost estimates need to look at the actual path vs just saying 5m/km is rediculus without any justification.