by tells us: 'That's the end of the penny section'...Whatever does this mean?

Never heard the phrase used personally, but I would envision it comes from a hundred years or so when a seat on the trolley/tram/whatever cost more or less, depending on where you were in the vehicle (front or back). And there would be a ?variable or fixed line of demarcation between the two, thus the "end of the penny section" and the beginning of the more expensive seats...how's my imagination?
(works just as well for seats in the theater, too.)