As my sharepoint experience is growing so just writing a post of how to create multiple port 80 sites or you can infact say web applications on SharePoint.
If you are familiar with the concept host headers that are used in IIS then it might seem very simple for you as it utilizes the same concept for running multiple web application on a single port 80.
so lets start, just open the Central administration console —-> Application Management—>create or extend webapplication
Click create a new web application –> fill all the fields & select port number as 80 and fill the host header. Click ok to proceed for site creation.
In this way you can create multiple sites running on port 80.