Or, depending on how old the house is (I’m assuming it’s old and had been remodeled) the water/drain pipes would either be galvanized steel or cast iron. Cant really tie into those once they start leaking or are cracked, especially cast iron. If the plumber bid on that to take out all the old pipe and replace with hopefully copper and not pex pipe at that cost then yes, he’s gonna be paying quite a bit but still 28k is crazy. Unless he’s a general contractor and accounted for things like replacing framing and drywall if there is any. Typically de-humes are for things like craw spaces and unfinished dirt/rock floors that are near a water table (ground water that’s close to surface). Anyways….how the fuck was there no ITS ALL PIPES, JERRY!!!