Not a Boffin,
You were comparing a US type UPC with a very different cost for Typhoon. I supplied a directly comparable figure.
Luckily, the UPC for Tranche 2 Typhoon doesn't need to be argued. The value of the T2 production contract was set in stone, and is known. Divide that by the number of aircraft and you have the UPC.
The NAO figure IS NOT A UPC.
We don't have a UPC for Tranche 3, but EF GmbH have always said that each successive Tranche would be cheaper in terms of UPC, and have succeeded in achieving that, so far.
With some UK-unique elements and weapons system costs included, RAF Tranche 1 jets cost £49 m or £45 m. Tranche 2 cost £42 m calculated in the same way. You might therefore expect Tranche 2 to come in at about £39 m on the same basis.
You won't save much by cancelling them.
F-35 is a different matter.
I want to save £1 Bn on Harrier, £5 Bn on ships (and we all know that they'll cost way more than that) and whatever JSF ends up costing, plus the high running costs.