If your CPC is $5, it doesn't necessarily means that you've been Google slapped. Look at your campaign. Maybe you are advertising something that is against TOS, or maybe your choosing the wrong keywords. To avoid Google slap, you will probably need a new domain.
One way to avoid a Google slap is to make sure you have basic pages on your site like privacy, disclaimer, terms of service, contact, about. So if you do set up a new domain get these sites (and some content) loaded before you get your campaign running. A few links out to other sites and a few links in doesn't hurt either.