by Jim » Mon Feb 11, 2008 10:02 am
Since the subtotal is a calculated price the only way to change it is to change something that is calculated into it. That would include deleting or adding products, reducing the quantity of a product, adding a coupon or qualifying for a reward that would make a product free.
If you had a product that was $1 then you could have the shopper add the number of items that they wanted so the total price would be based on the quantity they specified. (i.e. If they want to pay $10 they would add 10 to the cart.) If they want to reduce the amount they pay they could reduce the quantity in the cart.
If you want them to be able to make a donation you could have a variable price item included in the text of the shopping cart so that they could make an additional donation by adding that product to the cart with the amount that they wanted to give.