if you use google analytics it tracks every page for you..
then you look at your visits from google Paid ... this you should see (dependent on your sites setup) 3+ page views on average average time on site should be over 2:30 and your bounce rate should be below 50% if you have those you are driving the right visitors to your site and increasing the opportunity for the sale. these are general numbers and can vary but in my experience this indicates that you have driven the right visitors to your website.
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Click through rate is the number of times your ad is displayed to the number of times it is clicked on. This is how google judges you for quality and how much money you pay for your ads and the placement on the page. this is what Andy was originally referring too as that the costs have gone up.
To maintain a level that is going to drive business the costs have gone up!
You will be around 1.50 on high traffic keywords to maintain top 3 position if your ads convert.. You will be much higher if they don't... if you are paying less than this you are not getting priority placement.
I will be happy to help you more if you like... contact me directly.. this is not a solicitation just trying to help

-pg