rp_variable_price_heading

This filter is applied to use variable price heading, it is including one parameter.
$variable_price_label -> is containing post meta value of variable pricing lebel.

An example of how you can append is below:

function add_variable_price_heading( $variable_price_label ) {
$variable_price_label = //add variable price label.
return $variable_price_label;
}
add_filter( 'rp_variable_price_heading', 'add_variable_price_heading', 10, 1 );