Is it possible to find out a used car's MMR value?

Don't want to get too deep into it, but we are trying to replace our totaled van that we owed more money on than what it was currently valued. The company that financed the car says we need to use the insurance money to buy another car that has a similar MMR value to what our van was worth and already blocked us from buying a car we had picked this week because it was 1000 dollars less. Of course the other option would be to just give the company the insurance check and then pay off the remaining balance, but it would take a few months to pay off the difference and then we'd be stuck without a vehicle in the meantime.