I went with the Gibson Side-swept cat-back on my 1998 5.4L. Not too offensive sound-wise, but VERY noticible power increase. J.C. Whitney was about $289.00, installed it myself. Really easy to do. Alternately, header installation on the Expedition is a beast . God, what a job!! If they charge $300.00 for labor, it's probably fair. $180.00 for the muffler & install seems a bit high. I'm almost finished after two days...