Hemi engine maintenance

What is your question?

I am looking at buying a 2007 dodge durango with the hemi engine. I was told by one person that it is costly to maintain because spark plugs (all 16) must be replaced every 30,000 miles at a cost of around $400. Also I was told that the hemi engine cuts back to fewer cylinders when power not needed. Does this make it more economical on gas than a 4.7L engine?