Hear me out, if you think about gil in terms of yen, an 8 million yen 2-floor household seems pretty reasonable in the real world. Especially when you consider that a whole new room can be expanded for 850,000 yen. It also makes sense that depending on the market, Large Houses, aka Mansions can go for as high as 100-125 million yen which are realistically seen in Japanese real estate. Here are some examples I've looked up:

Small House

Medium House

Large House

To sum it up, houses are purely aesthetic, and while they may cost a lot, they're really supposed to. Housing is the largest investment you can make in this game, and was really implemented with the fact that multiple players would be paying the bill on the house. 30 million between 50 players is a measly 600,000 from each player.