Take a look at European high speed rail prices. They act similarly to airline prices, increasing close to departure to high levels.

What's that you say? You're in Manchester but need to pop down to London (2 hours 10 mins, 209 miles) tomorrow for a meeting? That'll be £338/$467.

The UK is not a good example on how rail systems can work. Rather look at France, Germany, Switzerland or Japan. HSR tickets in most countries have an upper limit, only the (partly) privatised UK system has these absurd prices.

You don't need to tell me, I live there :D

What's worse is that French, German and Dutch national rail operators have subsidiaries running rail contracts in the UK. So in a way we help fund the fantastic continental rail services...

But I understand that rail services on the continent are also heavily subsidised.

Depends on the system. In Germany, where you don't automatically buy a seat, you can hop on any train last minute at a high (but reasonable) price. You'll stand for the journey but in some situations I preferred that over some waitlist with an airline.

Take a look at ACELA, the last minute prices aren't that bad (well insofar as I missed my train and booked a seat on the next one with a minimal penalty - around $40).

True. However assuming the price of high speed rail tickets will be fixed because it is a public service, the government could similarly operate an airline instead of high speed rail using the same fixed price system. What would be the cost then?

That's not how Amtrak works now, they price it the same way as airlines, last minute is more expensive.

I'm in NYC and would never, ever fly to Boston or DC. For what that's worth.

Two points on this:

1. I'm not sure how that affects my point.

2. In my experience the price difference for last minute on Amtrak has been at most about 20% (though I'm not a frequent Amtrak traveler).