There is a remote possibility that Apple keeps the iPhone 18 at the same price as the 17, as regular iPhone shoppers tend to be more price sensitive than iPhone Pro shoppers. The could try to do what Nintendo did recently, and raise the price of accessories and other items more to keep iPhone pricing the same, but I don't think that would work here (there is only so much they could raise the prices for chargers, AirPods, smart covers, etc). Given that iPhone 17 already got a bump to 256 GB storage, I doubt they could do the same thing where they eliminate the lowest storage tier.
I don't think it's realistic to think that iPhone Pro pricing will stay the same. All major components have gone up in price, and they keep going up in price, and it doesn't make sense for any business to just absorb those costs.