complete website functionality

My project is more related to wedsite functionality. I already have the website and it is hosted by yahoo small business. All I need is for some one to add to this site. Make it more attractive. Yahoo allows you to add to the site. I know all of the functionality I want the site to have but I donot know how to add these things to the site and make them all work together. I have a estimating company called estimateexpress. I have a spread sheet that I put estimates on and make them available through the site. I need my customers to be able to register to be able to use the site so I need that functionality. There is a fee associated with registration so I need that functionality. The spread sheet would download directly from the site at time of purchase. It is basically an excel spreadsheet. I am looking for some one who is willing to work with yahoo support to finalize the site. It will be a clear and consice site. Not to many bells and whistles. I want some one who is creative not just some one who is only adding what I direct. I would also like this person to continue to work with the site after completion when things change and the needs of the site change. For additional fees ofcourse.