Depends on how you do it. I'm re-doing my '55 right now - but that consists of replacing the front two seat coverings with sport aircraft seats, new SCS vinyl flooring, stripping out and throwing away all the rotten 70 year old garbage, taking it down to metal and then painting, adding in 1/4" selkirk foam for panels, replacing and selling my aero fabricators extended baggage and ski tube with a airglas carbon fiber extended baggage, relocating the battery to the firewall - hopefully with earthX field approval but more likely with Atlee Dodge, replacing my ELT with a 406. Not even talking about the panel mods.
I'd say a reasonable estimate is somewhere between $500 bucks and $80,000.