Gift List function for existing online store

We have an existing custom built online store for a small retailer (2 shops). The site is written in PHP, Javascript and JQuery and used mySQL. This piece of work is to add new functionality, a Gift list feature to the site. Most of the code will be (or can be) completely separate from the existing code, but part of the work will involve modifying the existing shopping basket/checkout code. Some guidance to the existing code and coding recommendations will be available, but you should feel confident in your ability to investigate the existing code, which can best be described as being created by a gifted self taught individual. The requirements will be fully specified (See attached document) and will require no contact with the business users. You are expected to set up your own development environment to mirror the live one, and guidance on how to set up xammp appropriately will be given, along with the code and an obfuscated database. A test script will be provided for you to perform initial testing within your development environment, but you will not be expected to either install or test in the test environment, or install into live. Being a small business, this is very much a project "on a budget", so you can assume price sensitivity. I do require a fixed price, but in addition I need to know the number of hours that your price is based on. You will also need to agree to non-disclosure of the project details and client information.