What do you mean by "hackable price"?
One can easily download the source code of course...
He did wrap it in a frame or something to make it somewhat nontrivial.
<form name="_xclick" action="https://www.paypal.com/cgi-bin/webscr method="post" > <input type="hidden" name="cmd" value="_xclick"> <input type="hidden" name="business" value="sidana_01@yahoo.co.in"> <input type="hidden" name="image_url" value=""> <input type="hidden" name="cpp_header_image" value=""> <input type="hidden" name="currency_code" value="USD"> <input type="hidden" name="item_name" value="Drawing with jQuery on Canvas Script"> <input type="hidden" name="amount" value="10.00"> </form>