If you want to style your currency sign there is no class or element by default you can hook and style with css. Here's how to wrap it in <span></span> tags to be able to style the currency via css.

If you use english locale open: lib/Zend/Locale/Data/en.xml

Change this around line 3848: 

<symbol>$</symbol>
to this: 
<symbol>&lt;span&gt;$&lt;/span&gt;</symbol>

Thats it. Now the currency sign is wrapped in <span> tag and you can style it with css.

For example: 

.price-box .price span { color:red; font-size:26px; font-weight:bold; }
will make it red, big and bold.