https://techcrunch.com/2017/09/12/the-price-of-applecare-coverage-for-iphone-plus-models-has-increased/

Heads up if you want to buy AppleCare+ for an iPhone Plus: you’ll be paying more. The price of AppleCare+ for the iPhone 6s Plus and iPhone 7 Plus has increased to $149, which is also how much the plan will cost for the iPhone 8 Plus.

Previously, covering the two older Plus models cost $129, the same as iPhone 6s, iPhone 7 and iPhone 8. Owners of the latter three don’t have to pay more because the price of their AppleCare plans will remain the same.