This is so strange, I don't know how you're having this problem Norma. I just went into a new game, new lot, built a tiny house, and then went into buy mode and bought the most expensive items I could, including paintings and appliances. And then I clicked edit town, and the value was unchanged. And then I went into play a sim and have them call to "move" and see if the value would be different that way, and it wasn't.
If anyone else has any idea why this is happening I'm all ears!
The whole point of the rule though is to limit the amount that people can spend on their house. I want to put everyone on the same playing field as far as budget is concerned, so if you are getting a cheaper value, and then able to go back in and spend more money than everyone else, then that's a problem. Although at this point, I'm not sure how to fix it. I hate to make you re-do your work, so hopefully someone will have a smart idea on how to fix it.