If you find a truely rust free one at the right money then great, as often gets said the bolt on bits are cheap and plentiful, having owned such cars as capris, cortinas, and i am ashamed to say a nova i am of the opinion that unless you know and trust the person mending it you are better off repairing it yourself- my last cortina had been 'restored', resprayed, and flew through its m.o.t but was very touch and go in a lot of structural places within 6months....
also it depends on what you are willing to call rust free, personally i dont care as long as its straight and strong, i daresay theres a few mothballed pristine examples still out there but they will fetch bucks now, 20 years on british roads WILL have started the tinworm to some extent, the only question is whether you see it before yo hand your cash over.
i'll take an honest pig and a bit of work over an expensive one and the same amount anyday.