I have just added a cat back set up, with a magniflow. Is there anything else that I can do with out spending a lot money?
2008 HHR SS

 

Kind of depends on what you're trying to accomplish.
Looks, sounds, hp, handling? You didn't really say anything in your post.
Maybe if you stated "what" you're wanting from your car, we could give you some suggestions.

Fwiw. Look at mine(and others) signatures with the list of mods. It could give you some ideas.

 

So now it is loud, tune it, it should be fast too....