Price per quantity for custom fields

[zanardi]

I know there is a plugin to manage price per quantity in VirtueMart (and I already bought it) AND I know that since v2.0.18 multiple prices can be set for each product.
Now I have the need to set price per quantity for custom fields of "Cart Variant" type.

Example:

Range	T-shirt Price	Blue t-shirt Price
1-10	20	+5
11-20	18	+4

Do I have to write a VMcalculation plugin? Is there any pointer to similar plugins? Are there better solutions?
Thank you for any suggestion.

[servlet]

Just do it!