Hi minterthal,
I have read your project description, and I completely understand that there is already a PHP script (made by someone else, as seen in the link) readily available for free, and that you want to use the script ONLY for the calculated results to be passed back from a POST request in your page, ignoring the free PHP script's pre- and post-form pages. I am a highly experienced Web developer, and I totally get what you want to happen here. This is an easy job for someone who is a total PHP expert, and I just want to let you know that $250 is already enough for a project like this; you can ignore the higher bids. I am looking forward to working on this project. Thanks.
Respectfully yours,
Mark