It really comes down to if you are doing or having a shop do it. I had a custom downpipe done for my car, but it's the 4 cylinder and I'm not sure what the bends look like on the V6. I had a full 3" custom exhaust all done at the same time, but when I broke down the cost it came to about $500 for the downpipe including the cat. If you are doing it yourself then the costs is just materials which would be pretty easy to figure out.