Restaurant economics are a function of ingredient costs and labour. I suspect ingredient costs are close to OP's estimated multiples. But real wages are way up since the 1950s. Anything with a large labour component of costs will have tended to rise faster than inflation, which is an average of goods and services.
(There are specialised metrics if you actually wanted to dig into this question.)
Sorry, no. I'm saying labour is probably a larger fraction of the burger's costs today than it was in the 1950s. (I'd naively guess profits are, too.)
But labor costs certainly have gone up too.
What a specific purchase costs is highly dependant on the inputs, the cost of its labour (which might grow faster or slower than the average wage), and a lot of other factors.
Food is way more expensive today than it was 50 years ago. Airplane tickets are way cheaper. Everyone has a cellphone now, and middle class families have multiple cars, but a trip to the doctor will mean that ~15% of the population will be on the verge of not paying their bills. On the other hand, I have access to ~every major piece of music ever made for ~$15/month, so that's something.