I´d suggest you run a search terms report, within which you will be able to see what you have actually paid for clicks (on average) in relation to each actual search query.
With broad match keywords you can expect there to be a great difference between what search queries actually trigger your ads. And there might be a great difference in cost-per-click for those.
I´d also suggest you to add not only more keywords, but also the same keyword with different matching types.
So for example add "cheap cars in louisiana", but also [cheap cars in louisiana] and +cheap +cars +louisiana (the last type being modified broad match)
Also, have a look at your average position: does it vary a lot? You can get a better picture of this in the search terms report. Or, you can a rough picture of how often your ad was shown in the top slot at Google, and how often it appears on the side of or below the results. You can see this by clicking "Segment" (just above the graph) and choose "Top vs. Other".
There can be a great difference in CPC depending on in what position your ad appears.
Then I certainly recommend you opt out of Display Network and launch a separate campaign for that.
You could also segment your data wo see what costs clicks in each network accrued on average. Click "segment" (below the graph) and choose "Network with search partners"