As your site grows you will find maintenance becoming more and more of a problem (esp. if you want to change one of the commonly occuring elements like a link in your main naviagtion bar). Fortunately there are a few ways:
HTML editors
Some HTML editors will let you use find and replace across the entire site.
Includes
With includes you can have one file that contains all the code to build part of your page and then you include that in all of the pages where that part occurs. There are numerous solutions - both client-side and server-side and there are numerous resources which cover this topic:
