There is huge variability in Amtrak pricing. Peak trains will be pricier. That thrusday afternoon 5pm to BOS from nyp isn't available at $58 in advance like the same train on Wednesday. Prices creep up until travel.

Going from Stamford to DC, you'll likely hit high fare buckets as you are taking a seat off the bos-nyp and nyp-was. If you take a regional from Stamford to nyp and then the acela, you could save some money if the bos-nyp train is near full.

Peak Acela trains are full, but surprisingly there are a lot of empty seats on the train as it's just certain short sectors (out of nyp generally) thst are full.

Going to BOS, I've seen prices out of new haven been a lot lower on some trains, and taking a train going to Springfield or metro north could make the trip work when you can't stomach the fare Amtrak wants to charge.

I usually grab the acela if I can grab an early purchase fare, but otherwise the plane is faster and cheaper.

The AA return of the "shuttle" LGA-BOS generally has empty seats. If you are not travelling on opm, last minute award travel on aa miles or BA avios is a good deal.

If your schedule requires you to travel mid-day to the Boston area, the token gift to mass port flights to ORH are a cost effective option.