Most of the labor is getting the "valve covers" off and as pointed out the Driver's side is a PITA due to the "junk" in the way.
I have a bad GP at #! and #8 (so one on each bank but on opposite ends of the engine). I went ahead and bought a full set of 8 GP's (you can get them pretty cheaply but make usre you get Ford (ZD-11 or F4TZ-12A342-BAfor the 7.3L), as I have heard of problems with some of the "aftermarket" versions). I bought a whole set for $75. I have not tackled the job but all the estimates says 5 to 6 hours for both sides and all eight.
Also think about the interanal Electrical harness (F81Z-9D930-AB) that is under the cover as well. It get's "old" and stiff with age and heat so if you do have "connector" problems later, the labor would have to be redone. The harness is about $85.
I would reccomend if you crack one side, do them all and the harness. Provide your own parts and you can save a few $$$.
D