Hello,
I think this feature was already requested, but I will re-suggest it as i believe it will be better for the post ad page...
Instead of having to add a package for a free listing, why not just have a link next to the plan option on the post ad page, simply stating 'Free Ad Listing' with a checkbox, radio buttons or drop down menu for yes or no, and the price input will get disabled, (remember free ad?) and you can click the button to go on to next step?
Thank you
Brian