The housing market is player driven. The full price for the plot is squares problem and what square has in the game as a gil sink. I'm sorry if you do not like that but it is the way it is. If I owned a small house I could get 20-40 mil gil for it on my server as that is what the demand is.
They simply need to open up 8-10 more wards with nothing but small and medium sized plots in them.