Custom extension for WooCommerce wordpress shop

The project is to develop a plugin for an estore thats sells products in bulk quantities (50, 225, 6500 etc...). The pricing is flexible depending on the QTY. There is also an additional fixed price surchage on the product depending on options selected. We need a simple front end interface that lets the customer change the order QTY and see the price dynamically updated. Example of this is; [login to view URL] We also need the solution to have a simple backend plugin, that allows for the pricing to be easily entered. The site is built on Wordpress using the Woocommerce eStore platform. The solution would need to be a plugin. The designer needs to be UK based to take this project. Follow on work available if the project goes well. All questions welcome.