Making a mold of a full car is extremely expensive and time consuming. Do a door shell or even a corner for repair is doable but about the only cost realistic size. Kit Car magazine has done several article on pulling molds. For awhile on ebay there was a couple mould set in Texas --- but the smooth surface was messed up. I don't believe it ever sold --- wife wouldn't let me buy it for a yard decoration or hot tub.
If you did a mould of some of the addon pieces it might be worthwhile --- turbo whale tail, hard tonneau with head rest, hard top.