I've done both routes. If you have a hook up at a shop, then the custom route exhaust will be cheaper. Otherwise, you're spending at least as much as a decent cat back to have one built. If you have a custom exhaust built, do NOT let them use crush bends. Use ONLY mandrel bends. Crush bends can reduce flow by 25%. And if anyone tries to use a crinkle bend on your exhaust... Hit them in the head with whatever exhaust pipe you can get your hands on, and get your car away from them!!
In order of "OMG NO!" to "Yes, please!!"
Crinkle bends:
Crush bent:
Photo: Mike Kemper
Mandrel bends:
Photo: Mike Kemper
You can see that the crush bends are similar to the mandrel bends, but the size reduces for the bend. Mandrel bends are the same diameter all the way through the bend.