Add Bulk Price Discount functionality to catalogue

We need a PHP developer to Add Bulk Price Discount functionality to our catalogue, featuring over 200,000 items. Task includes website testing in checkout. We have 29 categories (see screenshot attached). We would like to be able to apply bulk discounts to each and every category (i.e. 5% off all Apparel). The discount will need: - allow discounts in either $ or % form (ie. $5 or 5% off) - allow admin to apply a start and end date Current ecommerce website in OsCommerce, custom PHP. Developer must be experienced in custom PHP. You are responsible to fix any code that you break in the process.