If you want to add a block after the price on the category page, and for this implementation, you can use the observer core_block_abstract_to_html_before.

You can implement the logic with the below steps:
File path: app/code/local/{namespace}/{yourmodule}/etc/config.xml

<?xml version="1.0"?>
<config>
    <global>
    <!-- ... -->
        <models> 
            <namespace_modulename>
                <class>Namespace_Modulename_Model</class>
            </namespace_modulename>
        </models>
    </global>
    <frontend>
        <events>
            <core_block_abstract_to_html_before>
                <observers>
                    <namespace_modulename>
                        <type>model</type>
                        <class>namespace_modulename/observer</class>
                        <method>insertBlock</method>
                    </namespace_modulename>
                </observers>
            </core_block_abstract_to_html_before>
        </events>
    </frontend>
</config>

The next step is creating the observer and your template file.
File path: app/code/local/{namespace}/{yourmodule}/Model/Observer.php

<?php
class Namespace_Modulename_Model_Observer
{
    public function insertBlock($observer)
    {
        /** @var $_block Mage_Core_Block_Abstract */
        /*Get block instance*/
        $_block = $observer->getBlock();
        /*get Block type*/
        $_type = $_block->getType();
       /*Check block type*/
        if ($_type == 'catalog/product_price') {
            /*Clone block instance*/
            $_child = clone $_block;
            /*set another type for block*/
            $_child->setType('test/block');
            /*set child for block*/
            $_block->setChild('child', $_child);
            /*set our template*/
            $_block->setTemplate('filename.phtml');
        }
    }
}
?>

You can add the template to app/design/frontend/<package>/<theme>/filename.phtml .
And finally, here is a template filename.phtml code:

<?php echo $this->getChildHtml('child') ?>