|Cost is based on each additional list. See two examples below:
Example 1: You placed an order with a single version of a letter which requires you to upload only one list. But you have 3 lists. Therefore you need to pay for merging two additional lists.
Example 2: You placed an order with two versions of a letter, which requires you to upload two lists. But you have total of six lists. Therefore you'll need to pay for merging four lists.