If you are using 14, you can hide a field. In Layout mode, In the Inspector go to the Data tab select the item "Hide Object When" You can use a formula like fieldname > 0. So if there is a value greater then 0 your field is hidden. This works for labels, fields etc.
In 12 or 13, you can use conditional formatting to make the text color match the background.
You can also hide objects with FM13 (at least I do with FMAdvanced)
You could also avoid repeating "included in cost" for every item with 0.
Filter your Lineitems portal on cost ≠ 0.
Calculate the list of items with cost = 0 with a SQL and if the list is not empty, set a merge variable on the layout to
"The following items are included in cost:¶¶" & ItemDescriptionList from the SQL.
Otherwise set it to empty.