I'm using Zen Cart 1.3.8a -

I'm stocking items that need to be priced differently depending on the quantity being ordered, i.e.

1-2 = £17.40
3-4 = £16.35
5-10 = £15.50

I want to customers to be able to enter the quantity of items they want in the "Add to Cart" box (e.g.. 4) and then the total cost be figured out automatically (e.g. 4 x 16.35 = 65.40)

I have so far only been able to use an option name set to "drop-down" and then setting up approriate values - but obviously this requires the customer to choose from the drop down which quantity range they are ordering and then entering the quantity of items they actually want in the Add to Cart box.

I'm sure I'm probably missing something incredibly obvious - hopefully someone can steer me in the right direction.