Hello,
The time for completing this project depends on the scope of the work that is to be done on the site. The dropdown menu can be difficult to implement, depending on the preferred look of the menu, browser compatibility issues, if you intend to have more than 2 levels of submenus.
The description is not clear on what else needs to be done on the site.
I have extensive experience with Joomla-based sites, have built 1.0 and 1.5 sites, functional side mainly. I can configure any type of joomla addon to accommodate your needs.
Best,