I haven't read most posts. Took amtrak with bike in 2021. Bike in checked baggage would have cost $10, not bad at all, but not able to be checked at smaller stations. You might be able to get off at a smaller station, I think I recall someone notifying the conductor beforehand and they were able to pull their bag off. Thus, I did this:



That view of the baggage shelf in the passenger car was on the way back. Outbound I was running a bit late and arrived at the station after bag check had closed, took the panniers off and folded the bike, got on board and put all in open (no-seats) area normally reserved for wheelchairs, never got hassled. Outbound was in "normal" passenger cars, return trip was on the taller cars with roof windows, supposed to be better, not really, AND, and the luggage area was at door level down the stairs, so at every stop I went down and kept an eye on the bike, lest someone quickly offload and make off with it.

Regarding luggage, I had both rear panniers strapped together as (#1) checked or carryon bag, both front panniers strapped together as (#2) checked or carryon bag, and a backpack as (#3) bag. I think you are allowed two checked bags and one carryon, that was my plan outbound but too late to check, and there was plenty of room in the car for all. Coming back I checked both sets of panniers and brought the bike and backpack on board.

Really easy, much easier than flying, requiring taking apart (even my folder) to meet checked bag size, put it in a bag, and then at my destination, if touring, figuring some place to stash the bike shipping bag. Problem is, about a half-day on the train was all my butt could handle on those hard seats. I'd like to do a train trip, with some train sections, broken up by days of biking, but may not be economical, versus flying.

Also, for both outbound and return, I had a shuttle bus out to the coast (incredibly cheap), checked beforehand that their bike rack could do a 20" wheel bike, yes. Get there, no. The bike rack holds the bike by the front wheel, and my front rack blocks that. No problem, folded the bike, brought on the shortbus with my bags, put in the wheelchair section, though could have also held it near my knees.