Create options with $0 price

I need to have some items at $0 price. I found in admin-woofix.js that I could remove the check for 0 price so I could enter zero prices. It seemed to work at first but then the dropdown dissappeared.

Here’s where I removed the check for $0 price:

$('.woofix_add_price').on('click', function() {
        var regularPrice = $('#_regular_price').val();
        //mark removed regular price check. original line below:
		//if (regularPrice == '' || regularPrice <= 0) {
		if (regularPrice == ''){
            alert ('Please add regular price.');
            return false;
        }

Can you point me to where else I should look to remove the checks on zero prices?