There is a sweet spot for purchasing Acelas at a decent price. You have to check often to catch it but it is somewhere around 2-3 months out. Some never drop but most do. There was a woman sitting next to me this afternoon who probably bought today (I always check if someone is sitting next to me before I board.... this morning there wasn't, an hour before departure there was) and if she did buy today she paid 4x what I did.

The RPA discount also gives 10% off. It's not much but it's something and supporting rail is a good thing in any case.