Custom Shipping with subsidy

I need a programmer to create a shipping module in Opencart. The specs are as follow; a. There is a fixed base-price for shipping, this can be set at the admin of this module. b. The incremental cost for each product is in the location field. c. Another field to indicate if the item is given free shipping (e.g. use Manufacturer Product Number - MPN) d. The shipping charges is subsidised by a percentage of the total order called the "subsidy factor". So the shipping cost = Base-Price + SUM(incremental for all non-Free shipping Product) - (subsidy factor) * (total amount for all non-Free shipping product). For example, Base-Price = $4.00 Subsidy Factor = 10% (Note these 2 parameters above are to be set at the admin module) Product Price Incremental Shipping Cost (e.g. using location field) Free Shipping (e.g, using “MPN” field Prod A $12.00 3.00 0 Prod B $15.00 2.00 0 Prod C $18.00 3.00 1 (i.e. FREE Shipping) Prod D $25.00 2.00 0 Prod E $12.00 1.00 1 (i.e. FREE Shipping) Cart Total = $82.00 So shipping cost = $4.00 + ($3+$2+$2) – 10%*($52) = $5.80 (Note those with free shipping is not included in the price computation). Refer to the PDF file if the words here are not formatted correctly for easy understanding.