You mean with "the line through" right? Something like a strikethrough?
Creating this with a plugin would be harsh as you could simply do this by altering the HTML code.
This sounds harder than it is, but the question is if you know how to alter an Arastta template !?

I am new to Arastta but as i have been playing around with it for some days now, here are my 2cents:
1. go to your template folder into the product folder (something like catalog\view\theme\TEMPLATENAME\product
2. Open category.tpl
3. Search a line where it says
4. Befor that line must be a code saying
5. Put this code within a or strikethough tag.

Greetings!

Greetings Carlos

Thanks for your input. However, it is not just a style change (which I can do via css). I need to display the regular price of the product and the discounted price of the product at the same time. Arastta can only display one price at a time as far as I know. Here is a picture of what I'm trying to achieve.