There are only a handful of things you can do within a campaign that will increase conversion rate. Most of the changes you may make within AdWords will effect your click through rate.
To really make strides with conversion rate you will have to make changes to your landing page and conversion page.
Do you have a strong brand? There is a lot of value in achieving brand recognition in your vertical by bidding on generic terms and converting a brand loyalist.
Many searchers will search for a generic term i.e. "Most reliable truck tires" and when they land on your site they might do some research, read your copy and make note of your brand. Then a week or two later when they are ready to buy truck tires they will search your brand keyword, land on your site and convert by ordering tires. This has the effect of recording a conversion on your brand keyword while apparently deflating the value of generic keywords, which receive less conversions.
If you're ad spend is less than $5000 a month, then $100-500 is fair price for an in-depth account audit. There are plenty of guys on here or in the marketplace willing to take a look at your account.
Good luck.
