Have you enabled the Conversion Optimiser on your Adwords account?
Instead of manually monitoring and adjusting your PPC bids, this tool now does much of that work for you. There are, however, as with all automated tools, certain things which do not work as well as human intuition, but on the whole this tool is likely to reduce your PPC costs and enable you to increase your conversion rates.
You can only apply it to campaigns that have had over 50 conversions in the previous month, so you may need to group together campaigns in order to reach the required conversions.
Interesting article here on SearchEngine Land about how and why it works with different scenarios, plus some results from broad match and exact match experiments.
If you are already using Google Conversion Optimizer, what are your feelings about its effectiveness for your clients or your own PPC campaigns?