A 2 mile, 4 lane vehicle tunnel in Seattle has cost $1.6 Billion per mile...Early estimates for the entire project Miami to Orlando was $3 Billion. In reality it will be closer to $4 Billion with Phase two coming in at $2.8 Billion or even a bit more, and won’t include the cost of Orlando Airport Mulimodal Center. That is a OIAA project. Brightline just leases space. Only cost of track is included. Phase one was a bit more than $1 Billion as I recall, maybe even as much as 1.5 Billion (haven’t seen the final numbers) though I am not sure what portion, if any, of Miami Central Station buildings is included. It probably includes the ramp and elevated tracks. They have in general run a tighter ship than usual.
https://en.wikipedia.org/wiki/Alaskan_Way_Viaduct_replacement_tunnel