Contact form 7 - how can i catch and customize each checkbox?

how can i catch and customize each checkbox in Contact form 7 plugin?

i have a list of checkboxes in a single field.

what i'm trying to do is to add an attribute and value using jQuery to each checkbox.

like this:

$("input['type=checkbox']:nth-child(3)").attr("data-price", 500).addClass("cf7-checkbox");

thanks so much!!!