The pricing system works exactly the same as it does for business class seats on non-Acela Express trains: a fixed accommodation charge for the service is added to the cost of the standard level of service on Acela Express (the standard or base level of service on Acela Express is business class) and linked directly to the availability of discounted inventories in business class.
Let's take a look using the example of a one way from Boston to New York on 30 December. First, here's the fare display.
At the top beneath "one way accommodation charge" you see P at $76.00. P represents first class, so the accommodation charge is $76 above the rail fare, or in this case, above the business class fare available
Below that appear the five different levels for business class on Acela Express, starting with $101 (DOAE) booked in KD inventory, all of the way up to $168 booked in K inventory. The $76 accommodation charge will be added to one of these fares, depending on the inventory available to sell. Available inventory of the five first class inventory codes matches their corresponding inventory codes in business class.
Now lets look at Acela Express availability on the 30th.
First class availability
Business class availability
The five first class inventory codes mimic the hierarchy of business class. PD (KD), PC (KC), PB (KB), PA (KA), and finally P (K) for the full fare.
Let's determine the price for a couple of these.
The first train, # 2155 at 7:15 a.m., has PD seats available (because KD is available) so a first class seat on this train would cost a total of $177: the DOAE fare of $101 plus the $76 accommodation charge for first class.
The third train, # 2163 at 11:15 a.m., has 5 PD seats available (because there are 5 KD seats available) and would also cost $177.
The fourth train, # 2167 at 1:15 p.m., only has P seats available (because all of the lower cost inventories for business class are sold out) so a first class seat on this train would cost a total of $244: the KOAE fare of $168 plus the $76 accommodation charge for first class.
The fifth train, # 2171 at 3:15 p.m., has 2 PA seats available (because there are 2 KA seats available). The price for a first class ticket would be $227 (the AOAE fare of $151, plus the $76 accommodation charge for first class).
The traveler, Anita Test, chooses the 11:15 a.m. departure and this is what her reservation would look like:
And the same thing via Amtrak.com:
Backward to # 14 - Fares, business class (Acela Express)
Forward to # 16 - Fares, sleeping accommodations