"BAE has said that they don’t know the exact cost of building such a ship in the UK." there is absolutely nothing they could use as a guideline"
But they are building carriers with nothing to use as a guidline !
The first bit is a blatant untruth. They had the data for the Waves, they just knew that they wouldn't have the capacity or be affordable. So they didn't bid.
The second isn't exactly true. The carriers are "just" complex warships (hoofing big ones to be sure) for which they've got plenty of estimating rates. There's nothing inherently different about them (other than size) compared to T45 for example.