With big projects, we quote the cost and that will be your cost regardless of the the number of hours involved.  Typically our customers will pay half to get their project started, and then the remainder once the project is complete.  Our quotes are based on actual experience installing systems all around town.  We know what it takes to get the job done and we will not take on a project unless we feel we can do the job right and be proud of what we accomplish.  In the end, we want our customers to be happy and feel that their computing environment is greatly improved.