There are several mufflers you can use - you don't need to buy the high dollar kits. All you need is a muffler with the inlet/outlet on the same side.
Spin Tech 333SCS mufflers are what I run on my side exit set up. They offered the most tq gain on a dyno and sounded the best. They run about $100 each, are a flat box design, so you don't have to worry about them dragging all over the place and will fit in the stock location. Any shop will be able to weld up to your Y pipe or cut it and weld in a flow pipe to each muffler.
I replaced the Magnaflow/Roush side exit mufflers with Spins on my V6. Best exhaust choice I made.
