Excellent question! Not to make money would be my first suggestion. Unless you have something pretty rare and valuable, I’m thinking 3.8 flat floor E type roadster, Aston Martin DB4, Lamborghini Miura etc etc then a full, high quality restoration on most classic cars will cost more than the car is currently worth. However, that’s not the way to look at it in my opinion. You may be personally attached to the vehicle, it may have been in the family your whole life, it may have always been a dream of yours to own this particular car. Then the cost is immaterial.
As we know, you can buy a new car for vast sums of money and within 5 years it’s practically worthless. A quality restoration will stand the test of time and they’re not making any more 1969 MGB’s with overdrive, or Jaguar E types, or Bugeye Sprites or TR3a Triumphs or whatever car you have. A properly restored car will almost certainly appreciate over time making it a better proposition than a new car.
I can promise you from personal experience that when you’re out driving your perfectly restored car on the open road you won’t remember the cost at all!
The other big (huge) issue is that when you restore it yourself, or have it restored, then you know exactly how it was done and the quality of the work. I can’t tell you how many “restored” cars I’ve seen that hide absolute horrors under shiny paintwork. It’s very difficult for an expert and almost impossible for the layperson to look at a nice shiny, freshly restored car and be able to tell whether the job will stand the test of time. It might seem cheaper to buy one “already done” but it is false economy if the paint bubbles up 5 years down the track and you have to pay to have it done properly. It happens and probably more often than you think.
Besides, a restoration project is fun, and sometimes heartbreaking… but mostly fun! Every car enthusiast should do it at least once!