Old car that runs well but with non-registration penalties; what to do?

I've owned this 1980 Volvo 242 DL since it was new and it runs well, the body is good and it has a nice interior. However, it's only worth about $1,000 tops on the car market.

I gave the car to my youngest son, but he failed to keep it registered. The DMV won't let him do a declaration of non-operation at this point, and they want $250 in registration and penalties.

How can I take back this car from my son while having to pay the minimum in registration and penalties, or am I SOL?

Thanks!