"The highest efficiency models can cost a little more up front, but
you'll save on fuel bills. You may have to shop around; some
installers may charge as little as $100 more for the high-efficiency
models, others charge a lot more. "

Anybody find that credible?

No. Either that or they are noly referring to the labor portion of
the install cost, and not for the equipment. I would not buy one of
these high efficiency furnaces simply because I don't run my furnace
enough to justify the cost.