98 Sienna uses Platinum plugs, approx. $6 - $10 ea. Iridium plug use on Siennas started with the VVT-i version 1MZ-FE starting in 2001.
a '98 Sienna more likely would need a coil pack than a wire, assuming the van is between 60k and 120k miles, if there really was a drivability issue. When one of these wires fail, it's pretty much an all-at-once hard misfire under load. I would suggest replacing the set (it is a set of three wires BTW) if one of them began causing a problem, or if the mileage was really high. Coil packs are about $90ish each and include the spark plug boot (which is what usually shorts to the plug tube and causes the eventual problem).
I get 2.0 hours at work (dealer). I take off the cowl which adds labor cost over a similar plug removal job in a 1MZ-FE equipped car. As with most things, do a couple and it's cake.
Not too bad to get at, maybe .5 to 1.0 labor depending on the shop.
Finally, I think the OP got his PCV and F/F prices switched.
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