Outputting a link as a button in node.tpl.php
This is what ultimately worked for me. I don't really understand it completely, but if anyone can shed some light on why it worked, I would really like to know.

&lt;a class="btn btn-danger btn-lg" target="_blank" href="&lt;?php print $content['field_amazon_link']['#items']['0']['url']; ?&gt;"&gt;Buy Now&lt;/a&gt;