I grew up in Saddleworth near the 3 stanedge tunnels, each around 3 miles long, soon after the canal tunnel was finished it became obsolete due to steam trains and a bigger rail tunnel being created. Then this tunnel also became obsolete due to a larger tunnel being required for diesel engine trains.
I cant afford the fares on current trains, I dread to think what HS2 tickets will cost. And with the introduction of self driving electric and hydrogen fuel cell cars, which take you from door to door with ease and less cost, and would also be quicker. Business people stopped using Concorde because it became obsolete after 911, you can do face to face with ease via computer, HS2 is obsolete before it even starts.
Given that 1 train driver and 1 guard can operate a train with up to 1,100 seated passengers compared to the same staff for up to 600 seated passengers, I would have thought that the costs of running the trains would be less.
The fact that those staff can operate about 4 return trips between London and Manchester in about the same time as 2 return trips, would further reduce costs.
Likewise you would require less trains to run the same level of services, further reducing costs.
Even if those traveling between the North West or the West Midlands and London (currently circa 24.5 million people/year) had to cover the cost of construction (with others, such as from Scotland, covering maintenance) over a 60 year design life it would cost £38 each (so a return of £76). Which isn't that far above the current £50 supper off peak tickets for London to Birmingham return, or that much lower than the £96 off peak return between London and Manchester.
That however doesn't allow for staff or train running (bus does cover the purchase of the trains), nor does it reduce the cost for Birmingham and increase it for Manchester or if people opt to go a different route. However conversely it doesn't allow for any future growth in rail passenger numbers or for passengers traveling between Manchester and Birmingham or any of the other cities/regions due to be served by HS2.
Anyway that long answer is just to say, there's probably nothing significant which would make the train tickets be that much different than they currently are. Unless someone can think of something.