Its Worth What it is WorthOver the years I have tried numerous optimisation strategies for Adwords Pay Per Click, in essence it should be simple and I'm going to take a simple strategy that I'm currently using on an account.
I have an account that has a target CPA of £10. So lets say the term 'widgets' converts at 0.3%.
So Max CPC = Conv Rate X CPA
Therefore in this case 0.03 (Conversion Rate) X 10 (Cost per Acquisition) = 0.33, (33p Max Cost Per Click).
It is not as simple as that of course you might find a term converts better in a lower position but at the very least you have a hard cap on the maximum bid.
I'm currently on working this into my Bidding Software System although you can use the Rules within Adwords itself, see screenshot below.