I need to pass emissions or at least visual inspection so I want to get test pipe made. I have a 3" dp which goes back to the cat back exhaust (no cat). I assume that the back foot or so of the dp should be cut and flanged for the test pipe and a new section with a hf cat and flanges needs to be made as well. How much should i expect to pay for this work at a good shop excluding the cost of the hf cat?