They are an expensive proposition as the entire bearing/assembly must be replaced. An independent shop could do this job for less I'm sure using aftermarket parts.
The high price does not mean you're being ripped off. The dealer labor rate is usually higher (out of necessity) and the dealer cost on the Genuine Ford OEM parts is usually pretty high. Tack on the dealer markup and the price at the dealer could be in line.
Usually bad bearings will either growl, rumble, and in some cases they may be quiet but the bearing/hub assembly has excessive play (looseness) in it. There usually is no adjustment on these and replacement is recommended if the play it outside the factory specs.
I would get another opinion, or two, with attention paid to bearing sideplay.
(For what it's worth, one of my daughter's cars (Mitsubishi) has the same type of bearing/hub unit and has excessive play in both rear hubs with no noise. How long it's been like that no one knows, but it's going to get repaired in the near future. At this point, no problem). Hope that helps.