Just more info...

1. You make a book on our website using our software. When you upload the book to our server, the URL will give me the product ID of the book you are uploading. The product id will contain the type of book ( hard cover, soft cover). It will also give me the number of pages. - 20 pages, 30 pages etc.

2. I need to give you the price of the book based on those two bits of information the software gives me.

3. If all I have is a product ID and the number of pages, can any off the shelf shopping cart have solution for me ?

How will I have to create a product Catalog?

Currently in my custom product catalog, I have 3 products :

Product ID/ Title/ Cost/ cost of each additional pages/
100/ hardcover book/ $2/ 0.20
121/softcoverbook/$1/ 0.20
133/Wirebound book/$3/ 0.20

Now, how will zen/ or anything work for me with this product catalog?

Please please please help me...i beg you....