The prices for a corned beef/pastrami sandwich are just crazy. You are right about that. My wife makes it at home and it's a lot cheaper!
You're a menschkeit, and because a lucky man to have a wife that can do that.

You're paying for the location, I get that in the city, also not a dime a dozen type food.
Many times those that frequent jewish delis are paying a premium because they are closed from hours before sundown to sundown Friday to Saturday, which is prime time in the restaurant business, and they do rely on not just "their kind" customer.
This Katz's deli goes 24 hours on Saturday, so not that....otherwise the corned beef sandwiches might be 40 smackaroos
