Not the US, but have _definitely_ noticed fast-food becoming prohibitively expensive here, over the last couple of years. To the point where I no longer eat it (a good thing, really, though the only reason I ever ate the stuff was because it used to be cheap).
Haven’t patronised any of the big name chains for a very long time, because the likes of McDonalds have always been very expensive. But I did use to sometimes resort to the cheap no-name chicken places that would do fried chicken and chips for £2. Those now have gone up to more like £4-5 so not worth the health-hit when they aren’t even cheap any more. I suspect many will go out of business, as being cheap was their USP.
Makes me laugh though that so often any criticism of the likes of McDonalds (for being bad for your health) gets a reaction that you are just being snobbish because ‘poor people’ eat at McDonalds, when in fact they have always been quite expensive. Heard the same with respect to criticism of supermarkets like Tesco,, usually coming from faux-populists who are too wealthy to notice that Tesco is actually quite expensive and relatively up-market.