The price I listed is for Iridium plugs for the V8, which are more expensive than the plugs the V6 calls for, but longer lasting.
Rockauto has K20HRU11 for $2.86 each with $5.99 shipping (to my zip code, anyway), so for 6 of them Amazon is $0.05 cheaper. Amazon builds the cost of "free" shipping into the price of some items. If you have Prime you're also paying for shipping with that, and if not then the free shipping is intentionally slowed down to try to get you to pay for faster shipping. I'll take 3-4 day shipping from Rockauto rather than 5-8 day shipping from Amazon for $0.05 more. I don't like Amazon that much for various reasons.