Back Office/ Product update, entry, deletion for a Magento e-commerce site

Thank you for looking at this project. I need someone familiar with Magento shopping cart to help with backoffice tasks. My products and catalog is not up to date. I need someone to go over all product lines and add/remove/update products accordingly. You will need to update the products from various manufacturers by looking at spreadsheets, manufacturer's site, competitor's site, etc. Please assume that there are ~ 500 products and bid accordingly. Not all products need to be updated. Please tell me what you are basing your bid on. Please also let me know how long you think it will take to finish. All deadlines are strictly enforced. If your score is less than 9 please do not bid Thank you