53 stations with a couple dozen robotic fare gates each sounds like about $3mil/yr to me.
If they really did it to stop fare evasion, it was ideological, not pragmatic. They spent pounds to save pennies.
Mass surveillance, on the other hand, is a motivation that makes sense, just not something you can really sell to the public when looking to spend a hundred million of taxpayer money.
On the other other hand, the kind of government that attempts to stamp out petty crime, at any cost, is the same sort of government that tends to want to surveil everyone.
They were teeing up introducing a "road pricing" scheme that would have also happened to record every vehicle trip on the local highways when their government was defeated.
And you assume the previous system cost $0 annually for maintenance?