I recently called BA to get an Avios upgrade cost for a Premium Economy to Club upgrade on a single leg YYZ to LHR.

The price I was quoted was 30k Avios and £300 which was explained to me as being taxes.

Taxes on that leg for cash fares are currently WT $CAD 65.46, WTP $CAD 65.46, CW $CAD 65.46

There's plenty of reward availability and the single leg is 60k Avios and £140 in WTP or 90k Avios and £175 in CW as a standard reward flight
Upgrading a one way ticket bought with cash at time of booking on the website is 20k Avios, £423 fare and £557 taxes and charges
Charges on that leg for cash fares are currently WT $CAD 297.50, WTP $CAD 470, CW $CAD 849.50

So how are the Avios and taxes worked out for these upgrades?