There's no direct "lose money" cheat, but motherlode accepts negative values, and spending is easy once you know how.
motherlode -50000 → Subtracts §50,000. Can go negative (red funds).familyFunds [Familyname] -100000 → Target a specific household.testingcheatsenabled true → Shift-click Sim → "Spawn" → "Sim Modder" → Set Funds to 0.testingcheatsenabled true → buydebug on → Buy Mode → Sort by Price (Desc) → Buy: Satellite Dish (§15,000), Weather Machine (§20,000), Generators, Sculptures.Open Neighborhood in SimPE → Sim Description → Family Funds → Set to 0. Save. Clean, instant, no cheat side-effects.
Note: Negative funds disable Buy/Build modes until positive. Bills still arrive; the Repo-man takes your best items.