The decision to see the CVA01 built would be hit with great force if making the Buccaneer for the RAF instead of the TSR2/F-111K/AFVG saga was cheap enough. That is by selecting the Spey-powered Buccaneer as the Canberra replacement at the end of the 1950s instead of merging the English Electric P.17 and VA Type 571 into the BAC TSR2.
However, I doubt that it would have saved enough money to prevent the cancellation of CVA01.
There is the story about Mountbatten going around with one photograph of the TSR2 and five of the Buccaneer claiming that one TSR2 cost the same as five Buccaneers. Though instead of the RAF buying 750 Buccaneers instead of the 150 TSR2s that were planned it is alleged that he wanted the RAF to buy 150 Buccaneers and the rest of the money to be spent on new aircraft carriers.
Following on from that...
At cancellation the projected R&D cost of the TSR2 was £270 million of which (IIRC) £210 million was for the airframe and £60 million for the engines and avionics. The estimated production cost was £3.4 million per aircraft. After adding the R&D cost in that meant a total cost of £610 million for a run of 100 aircraft and £780 million for 150 aircraft.
Note: The production runs of 100 and 150 aircraft include the 11 pre-production aircraft, but not the 9 prototypes whose cost was part of the R&D bill.
At the time of cancellation £125 million had actually been spent on the TSR2 but the cancellation charges brought the cost up to £195 million. About £45 million was spent on the F-111K before that was cancelled. Grand total about £240 million spent 1959-68. Which was a lot of money in those days.
My preferred solution is for the RAF and FAA to buy the OTL Spey Buccaneer airframe and engines fitted with a more advanced avionics package instead of the TSR2 and OTL Buccaneer S Mk 2 respectively.
The engine and airframe costs of the TTL Buccaneer S Mk 2 with better avionics have already been absorbed by the OTL Buccaneer S Mk 1 and S Mk 2. That leaves the cost of developing the more advanced electronics which in early 1965 would be estimated at £60 million like the avionics (and engines) for the TSR2. That theoretically leaves £180 million to spend on making the 150 production aircraft the RAF wanted to replace the Canberra.
Edit
Although the source I obtained the figures from claimed that most of the problems of the TSR2 had been sorted out by early 1965 so that the actual costs would have been the same as the latest estimates there is no guarantee of that being the case if the TSR2 had not been cancelled. So my estimate of £60 million to develop the more advanced avionics for a better Buccaneer S Mk 2 may well be an underestimate.
Also we can't be sure about the accuracy of the time estimates for developing the TSR2 and therefore the Spey Buccaneer with more advanced avionics.