The 1.9 150/6 speed auto is a God awful combination, speaking from three Months/20k experience in a replacement taxi when my Omega was first written off. . Don't think the 1.8 petrol is available as an auto.
All that said, the 2.8 Elite is auto only in Vectra C, Signum and Insignia... Which depends entirely on budget, but the Insignia adds 4x4 to the mix, and the Elite is a much nicer placer than any Vectrum
What did you find so disagreeable about it? Just slow, or something else? I'm not sure a 2.8's mpg & tax fulfill his definition of cost effective, but I will make the suggestion.
Just as you get to the torque band, it changes up. Manual shifting is automatically over ridden when the car decides, ie accelerate in M3, lift off for a second due to road conditions and re apply throttle expecting it to still be in third... Nope, it went to fourth or fifth.
Doesn't seem to be such an issue with the 2.8 in the Insignia. Only driven manual 2.8 Vectra.
Starter for a modest £4k..
https://www.autotrader.co.uk/classified/advert/201910193492820