Hi
It seems you want to use the extension as a shopping cart. Unfortunately , the extension doesn't support this . If you want to use it to sell products , only one product can be ordered one time (no shopping cart feature here) .
The extension has a feature called Fee Field . It allows automatically calculating price base on the value user choose . For example , you can create a custom field type dropdown, name quanliity with the setting like that :
+ 1 => $20
+ 2 => $40
.... and so on .
This method of price calculation is not very flexible. I will improve it in the next vesrion of the extension .
Thanks ,
Tuan