I'm not sure on the cost since I don't work on these things for a living, but it doesn't look too bad to change them. I would check at your local parts stores and dealers and with some of the sponsors of this forum for costs. Any shop can quote you the labor time to change them. They look easier to do than changing spark plugs in the 5.4L engines 04 and up.

 

They are easy to change. Autozone cost is around 25$ a piece. I've seen online costs of between $15 and $20 a piece. Ebay has a full set for $150. If bank 1 is where they problem is, just replace those four.

 

I will most likely just change the four on the passenger side ( bank 1 ) this weekend. I took truck back to shop w/ diagnostic machine and nothing came up. Better to be safe than sorry i guess.