The seals cost maybe 100 bucks for all 3, plus a rear gasket. They an be serviced without doing anything else to the diff plus 2 bottles of fluid. The VLSD coupler is a sealed unit inside the diff, it's not serviceable. The bearings only need to be touched if they are making noise and you are setting out to overhaul the whole pumpkin.
I replace external seals when needed and keep on keeping on.