Im re-ducting by whole house because the old duct work is old and leaky and to dirty to bother cleaning as I 2 have a full basement which allows easy access to do the work with out tearing down walls.
I would consider doing the job myself to save a lot of money if your handy. Home depot stocks all the duct parts. You may need to by one tool which makes crimps on the end of the duct to fit into another. Then seal the seams of the ducts with Mastic or GE silicon I or II. Its not as hard as you think. For more infomation on duct installation search on google.