Hi,
I checked your Excel Sheet. It's a pretty simple calculator.
I've built a Calculator [You may see my previous work on freelancer to be confirmed]. I built the calculator in such a way, so the owner can use it with any website built with WordPress.
I can build you the calculator all I need the calculation method you want in your calculator.
I'll also add the feature, after calculation you will have a nice invoice to print out [in case you need to give it to the customers]
Regards
Delowar