Content Management System Required

I want a new website for my business. Someone told me as my content keeps changing, to reduce the cost incurred while maintenance, I should go for some content management system. I am not sure what but someone told me Joomla. I want the bid to be reasonable and to be explained in detail. I will also like to know the time frame by which you can do it. I already have a template for my existing site that needs to be put on the new site. Happy bidding