We could add a checkbox, implying if it should be added after calculation of the product price, or before.
Hi Milbo,
I thnik lots of people need this option.
Actually as this thread explain it all, the final price never change even a custom price is apply, this is the "save" price that is bigger and bigger, and this is a nonsens IMHO.
100$ - 10$ discount = you save 10$ and you pay 90$
Add custom field option 100000$ = BINGO you save 100010$ !!! and you still pay 90$
Obviously there's something very wrong here...

And this bad behaviour wasn't at all with VM 1.1.9 for example
Found the Solution
replace the calculation.php file from
administrator\components\com_virtuemart\helpers\calculation.php
this will apply the discount to the base price and then add the custom field value
Thanks for the effort Kashif but it gives me a blank page
Thanks to all