I had 6.1 mil and change when I bought my small house, and I also bought one for my wife (She had around 400k).
Since then I've been bouncing around between 1.4 mil and 2 mil (currently at 1.9 mil), but I'm still testing out what furnishing I want, etc. I expect to bottom out around 1.5 mil at the lowest before I'm fully happy with my house.
edit: I want to point out that I don't go out of my way to make gil (I use the AH all the time, but I don't craft stuff to sell or SB for materia, etc), but I also don't buy a lot. I teleport all the time, buy from vendors when I'm lazy, and generally just don't put out more than I bring in from dailies/dungeons/challenge logs. I do dailies every day. Gil isn't hard to come by, and I can see how people might be rich as hell if they put effort into it. I'm also as of this edit 13 alexandrite from my novus which I had saved all my materia leveling up for, and have been playing for less than 4 months of subscription time.
