I wouldn't pay £80 for it. The paint finish is damaged and rust is peeping through -i you want a rusty bike you could buy something for a fiver.
Conversely, it is complete and original, so as a candidate for a restoration it's worth more than a junk shop snotter.
So, worth more than a heap, worth less than a really tidy one. £50-60 would be my limit - I've bought better spec Marins for not much more than that.