Actually it might be a feasible option for you. If you provide the piping and flanges, take it to an exhaust shop or a friend that can bend piping and knows how to weld. Then, all they are going to charge you for is labor. And how long can it really take to weld up a couple flanges? If it takes them an hour. Even at $120/hour you'll be coming out ahead rather than buying a prebuilt unit.
Plus you can say it's custom!!