New Free PPC Bidding tool

I've recently started running more PPC advertising campaigns on Google AdWords, and one thing that I always worry about is: "How high can I afford to bid on this keyword?" The last thing I want to do is run a campaign that loses money.

I seen tools that tell you your ROI etc, but I could find something that could tell me the max I could bid before I started losing money. I also wanted to find out what my max bid should be if I wanted to achieve a certain ROI.

With this in mind, I spent the past hour or so creating a tool that would answer my questions. I've uploaded it to one of my servers, and you are free to download an check it out. Please let me know what you think. I checked my math, but if you find an error let me know. I'd also like to know if there are other tools you'd like to see.

You can download the excel file at http://www.thebizbank.com/PPC-Bidding-Tool.xls