There are a few tools that claim they can report the cost of a keyword in the search engines. I can tell you with confidence and experience that none of those tools work. This is the case with both Google and Yahoo. There are sites like spyfu.com (subscription based) that can tell you the cost and words your competitors use, which it does neither well. Google Adwords has a tool called the "Traffic Estimator". The tool has you input a keyword, the PPC bid and the area which you will target (geo-targeting). The resulting report will show you the estimated clicks per day, estimated position and estimated pay per click. The report was very accurate with the estimated position and estimated clicks per day. One area that the Estimator was not even close was the estimated cost per click...oops. It was actually off $1.00 per click for certain keywords. A buck per click can add up fast, so that tool has been deemed useless.
There is only one true way to figure out the pay per click for keywords. Open an account and bid on the keywords. Take $25.00, pick a few keywords to test and set the bids at $0.50. Try to get on the first page so you can see the number of impressions (searches) for that keyword, and get a rough estimate on the price. The $25 - $100 you spend on testing keywords in the search engine will answer more questions than any of those sites that "report" PPC cost.