Unsolicited advice
We do run 500-700 for good 2.5" pipe with an x pipe, but I did install a TTI system on a car and it took 4 hours of my labor just to get it to fit DECENT. Then it leaked out of all the clamped areas and had to have it welded anyway. The cost of living is higher out here and these prices reflect the average cost. I have seen duals done for less, but the job was far from nice.