Open Source Awesomeness

WordPress Plugins are open source and you have the right to get them from the best available source. Don’t take our word for it, listen to the experts:

The license under which the WordPress software is released is the GPLv2 (or later) from the Free Software Foundation. A copy of the license is included with every copy of WordPress, but you can also read the text of the license here. […] Plugins and themes are derivative work and thus inherit the GPL license –
http://wordpress.org/about/license/

And if you decide you need support for your plugin purchase, you can purchase it directly from the plugin author.