You should actually be able to pick up a high-flow unit for much cheaper than an OE replacement would cost.
The Magnaflow/Carsound unit that fits your car can be had for 50-60 bucks as I recall. The exact part # escapes me, but if you do some searching in the Performance section for high-flow cats, you should find it. Or start a threar about it.
There are other cat options as well, Im running one completely different than everyone else here, but only because the Magnaflow I bought wouldnt fit, I also have a different exhaust setup under there than you do.
But I wouldnt get an OE replacement, its too expensive.
2000 Oldsmobile Intrigue 3.5L DOHC V6 15x,xxx miles "The Forgotten W-Body"
shaved badges, Eclipse HU, Pioneer TS-A1370R'*, Pioneer TS-A6971R'*, 20% tint, cleared corners, Silverstar Hi'*, 9005 Low'*
Fenderwell Intake, Hi-Flow Cat, U-bend delete, GMPP Handling Kit, MOOG endlinks, and 12-inch front rotors
1996 Bonneville SE RIP 157,751 miles, totaled 8/29/05