klier
Premium
A6 Avant 2.0 TDI: £35,000
A6 Allroad 3.0 TDI: £46,000
And the cheapest A6 Avant 3.0 TDI (quattro) is £43,000. So really, the difference is quite marginal.
The only difference is the A6 Avant starting with a 4 pot, and the Q7 with a V6. There's the price difference. But a model with the same engine costs roughly equal.