When fighting a war the numbers of ships are of critical importance and the way to achieve that was to keep size and cost to the practical minimum.
The T26 which grew like topsy till approx twice the size of a T23, one third larger than a T31 and that costs plus T26 as with the T23 designed as very quiet ships needed for their ASW mission which adds additional large costs, HED etc, etc.
Bottom line expect T26 platform costing twice if not more than a T31 before weapons and sensors added (Donald-san mention of approx £750 million each for T26 Batch II build).
PS V.Adm Gardner Director General Ships at Defence Equipment and Support interview four months ago said "T26 very, very complex, necessarily so for high end ASW, densely engineered, very, very expensive but wasn't something that could be afforded and sustained to deliver for the long term".