For the average car (ie, honda civic, nissan sentra) doing a conversion like this would cost about $1000. An Aston Martin Vanquish is not an average car. I would try contacting a performance vehicle specialist in your area and getting a ROUGH estimate. Perhaps if they have not worked on Astons then they have worked on other sport/super cars that may give you some sort of ballpark.
I would love to hear AM owners stories of the conversion if it has been done!