They don't. It's broken, lol.
My poor Astronaut has a crazy high bill because he has to have some stuff on his lot for his job, the game is charging him out the wazoo for these things.
Which is why I use the mod.
If you give your Sim the painter aspiration and then have them complete that and get them the reward that increases the value of these things? Your Sim will make a ton of money in just a few hours of painting. If you don't want to use mods to get the bills more reasonable. It's faster than collecting, IMO.