I have multiple prior experience with website building and database handling comprising multiple menus and dynamic content loading.
Depending on the further details of the sub-menu, design, loading and display options, I will design the sub-menu accordingly using preferable AJAX because of the feel attached to it and HTML, CSS for further displays. This all would take a maximum of 1 day.
You can contact me at akashperfect [at] gmail [dot] com