With something they used at the factory probably 50%. With something they didn't, maybe 80% loss. I'm throwing out numbers here. I'm no expert but I recall a few in that category not selling very quick.
Maybe on a rare custom color but a lot depends on the circumstance, Ren. If it is really worn or finish damage the value takes a big hit, even though original. A well restored pro refin may be 50% less than same condition original, maybe not, and could hold or exceed the original pre restoration value.