25-35 hours on a fully tig welded SS exhaust, with 4-6 V-band flange assemblies welded on (8-12 individual flanges), SS brackets welded on, nuts welded into the frame, etc.
Or for the cheaper jobs we take it down to the muffler shop and for $500 total get an aluminized steel, wrinkled, mig welded exhaust like Musclerodz said.
So it all depends on the fit/finish, and of course materials used. If we had a mandrel bender it'd take a fraction of the time!
If available, Stainless Works kits take a bit of time out since they mandrel bend everything and use slip-fit joints with band clamps. Those are only about $1000+.
-Dale