I have an '06 Ram 1500 w/Hemi (270K miles now). It takes me on average 3 1/2 to 4 hours to change out the plugs. I could do it faster if I didn't take so many beer breaks. LOL!$750 is high. Did mine a couple times, the shop manual calls for 4 hour and it takes every bit of it. I like the NGKs. What ever you do don't forget the ant-seize and use a tq wrench..
$750? Back in '07 my dealer only charged about $275 to change the plugs - after that I did them myself.