I would suggest a pacesetter y pipe which will convert to true dual. This will run you about $150. Then I suggest buying an inexpensive cat back, even an oem takeoff since your sixer will sound like ass to anyone within earshot if you choose a louder exhaust. Then take it to an exhaust shop if you can't install it. I'm guessing around $450 for all that.
What I did on my old '01 was buy a GT take-off catback(these were still plentiful in 2003), then I bought 2 MAC Flowpath mufflers to replace the OEM ones. I had an exahust shop made an H-pipe to connect it all after the cats, and weld it all together. After parts, shipping, and install I was in about $430.
If I did it again, I'd just get this: http://www.americanmuscle.com/99-04...um=Shopping&AMID=99-04-v6-mac-catback-2000-V6
You can install it in your driveway on ramps and jackstands. And if you decide to go True Duals later, you can simply have a shop cut the y-pipes out and fabricate and weld in a new mid-pipe. I wouldn't worry about it being True duals unless you plan on doing some extensive mods to your engine that are going to greatly increase the amount of exhaust coming out.
As for sticking with OEM mufflers because the V6 "sounds like ass." That's relative from person to person. I've heard good sounding V6es with MAC and Flowmaster mufflers, and I've heard crappy V6es with cherry bombs or fart can mufflers. I've also heard some pretty crappy 2v 4.6 v8's with aftermarket exhaust. The only crappy 3v 4.6 I've heard had Pypes mufflers and sounded like raspy ass. Point being, you kinda have to match the muffler to the motor.
I'd go for something mellow, but not just outright LOUD, like the MAC Flowpaths; they won't be raspy with the V6.
I installed a Magnaflow kit on my 01' V-6 and it sounds good. I modified it so it would fit the GT rear valance as the Magnaflow dual kit for the V-6 assumes you have a stock rear valance. the Magnaflow kit was about $495.00 if I remember correctly.