If money is no issue, go to Summitracing.com and order all Stainless steel 180* and 90* bends as well as some straight sections. They also sell completed y-pipes as well. they are all mandrel bent and pretty cheap for what you would see them anywhere else. then you can have it all cut and fabbed up at a muffler shop.

I just did this sat for the rest of my exhaust for my MR2, i bought all mandrel bends in 2.5" 18 gauge steel, 2.5" high flow cat, 2.5" Dynomax muffler, 4 2.5" flanges, 3 stainless hangers, and all the hardware. All that cost me $210