The Ford engines have a Problem with spark plug threads being pulled out of the head while removing the spark plugs, Ford recomends replacing your spark plugs every 100,000 you in reality should replace them at 60,000. Reduces the chance of the plugs ruining your threads which require additional labor and thread repair kits as much as 125 per cylinder.
This can be a tough job. Many ford technicians I know actually remove the cab of the truck so that they can have better access to the spark plugs. I would also recommend re-threading the spark plug holes (ford sells a kit - but its not cheap) because the engine in your truck is known to "spit plugs" - meaning: tear the threads out and fire a plug. this is no fun. Obviously I havent looked at your truck, but if the shop that gave you the estimate is one you trust, I dont doubt that the estimate can be that high. Ask them if they have done many. For your peace of mind, its NOT just a normal tune-up :) good luck
f-150 models prior to 2003 had a shorter thread count for spark plugs required. this design flaw made them brittle causing breakage. in 2003 ford addressed the problem by redesigning for a longer thread count spark plug. the never seize recommendation is a good rule of thumb. just be gentle on removal of old plugs. you may also notice excessive wear on spark plugs and coil boots on the left bank. this is due to exhaust configuration. recommend upgrade to dual exhaust system to balance exhaust flow. you get better sound and increased torque from third to fifth gear.