I'm doing my dump to tip in 4 inch at the moment.$710 for two SMB mufflers at my size (the biggest I thought I could squeeze in there).
$435 for 6 m of 4 inch tube, 3 90's, 4 45 degree bends and a 3 to 4 inch expander.
Labour to do it, not sure.
Few bucks for hangers.
You only wanting a car back should be done in 4 to 5 hours with a good operator and half the amount in material.