Hi Jonas, we can't help you with "how do i...?" questions (hellothemes.com/support-policy) ,but as an exception:
You have to edit this file: app/design/frontend/default/hellotonic/template/catalog/product/slide_products.phtml
Add this line below the h3 class="product-title" line 56:
<h3><?php $price = $_product->price; echo number_format($price, 2, ',', ' '); ?></h3>
Omit the / before quotes, since it is an issue in the text editor, sorry.