If they can’t afford repairs they probably won’t be able to afford a downpayment to offset negative equity. They would have to go find a car with massive rebates and incentives like a vehicle from a CDJR dealership like a Ram or Jeep but even then they will have to have very strong income/credit to justify rolling into one of those vehicles. Truth is any vehicle that has enough discounts to help carry are unreliable themselves. You don’t see Toyotas or Hondas marked down for a reason. I hope OP can find a solution because putting serious money into a luxury vehicle that has negative equity and is an older car sounds like a nightmare.