Do you use mods? Here's one random quirky suggestion and 2 practical ones.
1. MCCC has a child support system. If your current heir is a cassanova and you're on a 100 baby challenge, you could have him make a ton of babies outside the main household and send child support money their way. I think it's set at 1% of total value per child (which you can tweak for more if you want). I've personally never tried this, only saw it in the control panel.
2. Have you tried
SNB Bills mod? You'll have to pay property taxes. Also separates utility bills into water/electricity/etc so your bills might increase.
3. Buy the most expensive mansion and pay hefty bills. I just downloaded a 1.5mil venue from the gallery yesterday so that's one way to lose 15% of your money fast.
