Originally Posted by RobBeck
Brand new OEM units are about $600 each which is a great deal if you consider that they are brand new and come with brand new Internal wastegates and wastegate actuators. You can rebuild your CHRA's as well, for about $250 or less, but are still left with a rebuilt unit with potentially very worn wastegates. All in all, if looking for on the cheap, I'd just bite the bullet and get brand new OEM units from Tischer or the like. Some would even be interested in your cores for maybe a couple hundred and the condition in that situation does not matter.
On another note, there are other things that can contribute to smoking out the exhaust, but turbos is definitely a possibility as well.
+1 I swapped out my bad stock center sections to ones with around 10k miles on them onto my 29k old stock units, cost including labor was 200 bucks.
After watching the guy do it, I believe swapping centers is a diy provided the turbos are off the car.