Charles Darwin wrote: "The number of large houses and other buildings just finished was truly surprising; nevertheless, every one complained of the high rents and the difficulty in procuring a house."
Some things never change. Rents always feel high if you're paying them, as does mortgage interest, but they're both obviously limited to what people are earning.
Over time, though, you'd expect the earning power of property (the rent it can generate—or save you if you live there) to rise roughly in line with the growth in average wages.
Over the very long term it has to be this way - it's not possible for people to pay more than their income in rent. In its 2001 yearbook, the Australian Bureau of Statistics (ABS) published a book full of statistics regarding the previous century of federation.
Figure 1: A century of rent.
Average weekly earnings (2001 dollars): $217.50 (1901), $830 (2001)
Average rent on a 3 bedroom home (2001 dollars) $65 (1901), $250 (2001)
% of income spent on rent: 29.9% (1901), 30.1% (2001)
Source: ABS
The average weekly wage for an adult male grew from "$4.35 for a working week of almost 50 hours, which after inflation equates to $217.50", to "$830.00 for around 37 hours work, in far better conditions."
So salaries averaged annual growth of 1.35% over and above inflation.
When it comes to rent "the average weekly rent for a three bedroom house in 1901 was $1.30, equivalent to about $65.00 today. The actual value today varies depending on location, but the average of eight capital cities for a three bedroom house is about $250 a week."
At 1.36% per year, the average growth in real rent was almost identical to the growth in salaries. It seems a fair assumption that this relationship will be maintained.