Unusual discount question

[Athens Collectibles]

I use Zen Cart version 1.3.9h and have an unusual question, to which I couldn't find an answer in the forums, tutorials or FAQs. I wonder if somebody could help by suggesting a solution or perhaps one of the free add-ons.

I have a category called ART populated with products
A ($100)
B ($200)
C ($300)
D ($400)
E ($500)
F ($600)

What I want to do is give a discount of 15% if a customer buys any two products, 20% if he buys any three products and 25% if he buys any four or more products.

The requirements are:
- The offer applies to the specific category only
- All products are unique and their quantity is therefore one. This rules out the quantity discount.
- The customer can buy any products of his choice from the category. This differs from the Amazon-style of getting a discount for buying (for example) A+C or B+C+E together.

Hypothetical purchases could be:
Item B only - price $200 - no discount
Items A+C - price $100+$300=$400 - discount 15% - net cost $400-15%=$340
Items A+D+E - price $100+$400+$500=$1000 - discount 20% - net cost $1000-20%=$800
Items B+D+E+F - price $200+$400+$500+$600=$1700 - discount 25% - net cost $1700-25%=$1275

I have considered discount coupons but the percentages are different (from 0% to 25%) depending on the number of items purchased. I also considered product options but a number of 10-15 products would require a huge number of options for each product. To give an example based on the six products listed above, some options for product A would be: A, A+B, A+C, A+D, A+E, A+F, A+B+C, A+B+D, A+B+E, A+B+F, A+C+D, A+C+E, A+C+F, A+D+E, A+D+F, A+B+C+D, A+C+D+E, A+D+E+F and a lot more.

I'm probably asking too much but post this in the hope that somebody might have faced and solved it before.

Many thanks in advance for any assistance and best regards.

[stevesh]

I haven't used it, but there's this:

http://www.zen-cart.com/index.php?ma...roducts_id=235

swguy specializes in discounts, so there may be more on his site, if that doesn't do it.

[Athens Collectibles]

Thank you for the quick response. I will check this add-on and see if it can be used in my case.