Upper floor apartments were cheaper because they were meant for working-class people. The ground level and first floor were for shops and shopkeepers. The 2nd floor (that would be the 3rd flood in American terms) was the "noble" floor for rich people, with high ceilings and big balconies. The last floor under the roof was for housekeepers and cooks of the rich people below.
Well, I think the causality is the other way. The builders had good reason not to build giant penthouse apartments with views at the top: they knew their customers' preferences!
Obviously there were no elevators.