Don't bother with a second hand OEM, you'll only have to end up getting another down the line. Get a new one. As Gareth said, it shouldn't make it any louder I don't think, or not by much. I went with an "eBay special" and I was pleasantly surprised.
Got mine for £80 delivered in an auction, turned out to be a Japspeed one. Fitment was good and it is of nice quality. Feels like I have more power now, although my exhaust has been blowing for a while though, so might be in my head lol. All depends on your budget