There's a lot to consider, the size of the house, access, number of fixtures, fixtures require changing? Contractors are hungry right now you can get some fairly good savings.
RESEARCH your contractors! Make sure they have at least 5 years on the license! Have I seen some really bad things by done licensed contractors.
Workers Comp, Liability, referrals!!! A couple of hours can save you months of headaches and loss of $$$$$