When I did mine, I went ahead and purchased a pacesetter header, I know I got it for less than $200. I then had the entire restrictive system replaced. I think it cost me less than $300 + the cost of the header for a new setup including cat and O2 sensors.

2000 Chevy Tahoe nothing special. 1990 Isuzu Amigo, 3" lift, 31x10.5x15 BFG All Terrain (Street), 33x12.5x15 (offroad), Pacesetter header, some ATM rash. More mods to come......