Amsoil is pricey, but it's not supposed to be changed like other oils. Instead of changing the oil every 5,000 miles, you're supposed to do periodic testing of the oil. They have test kits for this; you send a sample of the oil back to Amsoil, and they do an analysis and tell you if it needs to be changed. IIRC, when I was running Amsoil, you could go up to 25,000 miles on the oil, with a filter change at 12,500mi, but it's been a few years since then.
Mobil1, even the 5W20, is a heck of a lot easier to find, so that's what I run. FWIW, Mobil1 claims that it meets the Ford specifications right on the bottle.