Match an ID and do something
HTML
<div class="form-item" id="edit-field-rates-0-weekly-rate-wrapper">
content 1
</div>
<div class="form-item" id="edit-field-rates-1-weekly-rate-wrapper">
content 2
</div>
<div class="form-item" id="edit-field-rates-2-weekly-rate-wrapper">
content 3
</div>
JavaScript
var weekly = [];
$("[id$=-weekly-rate-wrapper]").each(function () {
weekly.push($(this).attr('id'));
});
// do something
alert(weekly);