Basically it’s not going to happen, no matter what any of the “for” team say it is just not financially viable.
I work in the signalboxes in the the area and predominantly in the ones around Buxton and have done for the last 12½ years so have a pretty good idea of how things could and do cost and if people were alarmed at the cost of HS2 then the cost of a small single line will be very upsetting!
For a start the tunnels would need a lot of work, the existing ones around the quarries in Dove Holes and the main line towards Edale are constantly being maintained at the weekends so there is a lot to catch up on there.
The line is only a single line and if reopened the main aim would be, as others have said, to get freight not only off the roads but off the Hope Valley lines where it causes a lot of delays to passenger services so running passenger trains inbetween would be next to impossible other than the odd weekend only service.
Then you have to take into account not just the cost of re-railing, ballasting, signalling (which includes all the communications and cabling), new signalboxes, staffing (would probably be a couple of grade 3+ boxes required, at least 3 staff on £45k+ wages) not to mention the upgrades required at Buxton Station to link everything up.
Now baring in mind just a refresh of an existing signalbox alone can cost upwards of £250,000 (believe me, I don’t know how it is possible but….) you’re talking easily upwards of £25 million just to get the grass roots laid which would never, ever be recouped with the traffic that could be expected.
TLDR, the potential benefits vastly underweigh the potential costs.
