Hi. I'm a full time developer in the UK running my own company - Rocket Sites Ltd - that specialises in Zen Cart development. I've been working with Zen Cart for over 8 years, and I'm afraid to say that what you require cannot be achieved with such a low budget. My bid covers achieving the dynamic pricing using jQuery and following all Zen Cart best practices and auto-loading protocols, meaning that your Zen Cart version can be upgraded safely in the future without the risk of losing the custom work.