A quick google on "DB5 for sale" reveals:
2 on carandclassic.co.uk - at £650k and £485k
A convertible at Aston Workshop at £899.9k
One on Classic Driver at £625k

So, allowing for Journalistic licence (20% minimum) £1m is not far off.

Paul
Costock, UK
Plus Four 75th - Furka Rouge - Pip
Disco 5
Teddy - 17h1 Irish Draught cross