there are no HTML attribute associated with price for those listing . what you need to do is to add html attribute for the price and then use CSS to style as you need.
i show you how to do this for Product All listing . I assume you know enough about Override . Override tpl_modules_products_all_listing.php
look for code on line 79 and add the change in Red to your code
$display_products_price = TEXT_PRICE . ' ' .'<span id="PriceAll">'. $products_price .'</span>' . str_repeat('<br clear="all" />', substr(PRODUCT_ALL_LIST_PRICE, 3, 1)) . (zen_get_show_product_switch($products_all->fields[
I added Id to this span, you can remove it if you want
you can do the same with other template files
in your CSS you can use the span id to change font size , etc or you can use parent child relation to do the same .
#PriceAll {
font-weight : bold ;
font-size : 1em ;
}
or if you remove span ID , then you can use this in your stylesheet
.main span {
font-weight: bold;
font-size : 1em ;
}