Well I think it's more of a case they'll paint it properly and it'll be baked on rather than just sprayed from a can. I've tried using these rustproof things you can get from Halfords and then priming and painting it with cans but it just doesn't last, you can always tell it's been done, and the rust comes back through really quick. They're a waste of money really, especially on something like your car it's best to have it done properly.
Best to just get a few quotes from paintshops mate, I'm not a sprayer (a mate of mine is though) so I can't really judge it and the shop would need to see the car to see how much work was involved.