I think the resonator is esentially another muffler (just smaller) in series with the main muffler to dampen the noise even more. Surprised that it is more $$$ then the muffler. On my Olds the resonator is smaller and much cheaper.
Another thought is why are so many of you replacing your exhaust components? Aren't your Stainless steel. They'll last forever as long as you don't run over a curb and tangle it up=.??
'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)