Cost per square inch calculator


I'm need a php script that will enable me to calculate pricing for our materials.
It will be based upon $ per each square inch. The square inch pricing will gradually go down for larger items. I need the following increments that are listed below:
$01.00 for first 6 square inches.**
$00.15 each additional square inch up to 7-25 sq in.**
$00.14 each additional square inch up to 26-50 sq in.**
$00.13 each additional square inch up to 51-75 sq in.**
$00.12 each additional square inch up to 76-100 sq in.**
$00.11 each additional square inch up to 101-150 sq in.**
$00.10 each additional square inch up to 151-200 sq in.**
$00.09 each additional square inch up to 201-300 sq in.**
$00.08 each additional square inch up to 301-500 sq in.**
$00.07 each additional square inch up to 501-1000 sq in.**
$00.06 each additional square inch up to 1000+ sq in.**
So, the script will calculate the grand total of the cost per square inch. So, for example, if I have a sign that is 11 inches width by 33 inch height, your script will have width by height fields to enable me to put in these dimensions and will calculate the cost of the first 6 inches + the other increments and add them up to get a grand total. In addition, I will be able to configure a difficulty multiplier that will increase the grand total by a certain amount based upon difficulty. An example is listed below.
Difficulty multiplier
Normal (x 1), Complex(x 1.10), Very Complex (x 1.25)
I will need an online configuration page (protected by password) that will let me update my square inch pricing and difficulty meter multiplier when needed.
I have a GoDaddy web server and it will need to be installed and configured on that server.
Legal:
1) I require complete and fully-functional working program(s) in executable form as well as complete source code of all work done (so that I may modify it in the future).
2) Deliverables must be in ready-to-run condition as follows (depending on the nature of the deliverables):
2b) Any website server-side deliverables must be installed by the worker in ready-to-run condition in the employer's environment.
2c) Any website server-side deliverables must be provided with complete instructions and assistance so that the employer may install them in ready-to-run condition in the employer's environment.
2d) Any website server-side deliverables must be installed as described elsewhere by the employer.
2e) If there are any server-side deliverables (intended to only exist in one place in the employer's environment) then they must be installed by the worker in ready-to-run condition (unless specified elsewhere by the employer).
2f) All other software (including but not limited to any desktop software or software the employer intends to distribute) must include a software installation package that will install the software in ready-to-run condition on the platform(s) specified in this project (unless specified elsewhere by the employer).
3) All deliverables will be considered 'work made for hire' under U.S. Copyright law. Employer will receive exclusive and complete copyrights to all work purchased.
3b) No part of the deliverable may contain any copyright restricted 3rd party components (including GPL, GNU, Copyleft, etc.) unless all copyright ramifications are explained AND AGREED TO by the employer on the site per the worker's 'Worker Legal Agreement'.
Detailed Requirements:

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