The iPhone 6 Plus and iPhone 6 have the biggest screens of any iPhone, and they're bringing with them the biggest out-of-pocket replacement cost too. It's not terribly surprisingly that it could cost more to replace a high-resolution 5.5-inch or 4.7-inch phone over the smaller previous iPhones, but if you happen to break yours and need a replacement, it will cost you a pretty penny (or two).
So just how much? An iPhone 6 replacement will run up to $299, while replacing an iPhone 6 Plus hits $329. Of course, that's better than paying full retail cost for a replacement. And this is for out-of-warranty expenses, i.e. you broke it, not just something went wrong with it.
As for screen replacements, if you do have AppleCare+, Apple will charge $109 for an iPhone 6 screen replacement and $129 for the iPhone 6 Plus (strangely, the iPhone 5s, 5c, and 5 also run $129 per screen under AppleCare). If you have AppleCare+, that runs a standard $79 for the first two incidents of accidental damage, regardless of if we're talking about replacing a broken screen or replacing a demolished phone.
Our recommendation: don't drop your phone in the first place.