Some ideas could be selling cooked dishes for 50 to 75% rate right in a yard sale or at a festival. The kids can help sell that. Combine that with fishing for Sturgeon fish valued at $2k to $3k with all the adult/young adult sims could help as well. If you know how to collect the ingredients for ambrosia, that would give you up to $75k too. Additionally, selling paintings at a festival could earn you up to $15k or more a piece depending on the skill of your Sims. If all else fails, you should just downsize or trade out more expensive items such as beds, tv's, and computers in favor of cheaper ones or rent out some basement space to other working Sims.
Btw, in the future, buying a business first is probably a better idea than buying an overpriced house first. Then you know you will have sustainable income. Interestingly enough, one of my Sims earns her money even when she is not at her boutique and it seems to always be just enough to cover her bills. Not bad!