A lot depends on where you live. We can point you to some good prices on line, but sometimes shipping is unreasonable.
We like Auto Nation White Bear Lake (or Tasca).
Part number: 5C3Z-9C968-CA
2005-2010 Ford part # 5C3Z-9C968-CA - IPR, 6.0, fits 05-07 (CM5126)
Sometimes, FordParts.com can get you the same price and delivery is free if you select to pick it up at a local dealership. From what I see on the IPR, it is too high through them ($275).
Rock Auto is $153, and I know they are popular, but for some reason I struggle with decisions on buying their stuff. Can't explain why, but I would rather spend extra at an on line dealership - at least on electronics. That said, $50 is a nice sum to save.
Extreme Diesel is another common choice, but they are a bit higher than ANWBL.