We have a ledger attached already; does this save any cost?

Not Really. Usually the home builder slaps up a ledger for the benefit of the siding people. They are hardly ever attached properly.

This is the place where most amateurs mess up. An improperly attached ledger is very dangerous, and the flashing over the top is critical to prevent leakage into your house. I don't charge to do the ledger anyway, its just part of the set up and not significant in the total cost of a deck.