I recall researching those about 30 years back. And reading that they are explicitly outlawed in the US.
Check out the Skunk Train rail bikes in Fort Bragg California. https://www.skunktrain.com/railbikes/
https://www.abc10.com/article/news/local/sacramento/railbike...
They started off at $50 per person on a two-seater railbike, but went up to $250 for the bike ride (so a 150% increase from $100 to $250, or 2.5x increase).
The explanation was along the lines of "it's what the experience costs, we started off low to gain some steam, but adjusted to actual price later". Their railbikes have electric assist systems too, and the rides are around 90 minutes.
And in some cases the available route length is quite a bit longer than the seven or fifteen miles mentioned in that article.