Depending on the engine (V-6 requires removal of right drive shaft, lower ball joint, and exhaust y-pipe...) it should take a couple of hours. Ford OEM alternators are more expensive than aftermarket, and a independent shop may have a better price.
I replaced mine (V-6) on a Saturday (took me all day). The rear support bracket bolts are tough to loosen and you have to wire together to ends of the driveshaft and support the driveshaft while it out the CV joints will separate. Don't forget to check the serpentine belt while its out.
