if you have a idea to pay % value of anything its a money sink, not "money rape" what ever it means.
You would find players losing all vehicles they own in case they cant login for a month, ok losing property's in a limited market is acceptable, because it makes room for more active people.
losing a thing, only you can use, and drive unless you are sharing a garage is kinda dumb, it has no purpose, you will gain the 80% of the vehicle value, and lose the 20, this is not like houses and biz, where you get 100% back.
Simply said this idea will chase away all players who lose there vehicles.