Good find, thanks for posting Ash.
After reading the article I've just worked out how much a 400/4 would cost today taking into account the inflation costs using the Bank of England inflation calculator. The model was introduced in March 1975 @£650, in todays money it would cost a staggering £5,356.23! This price indicates a fully restored 400/4 @£5k as a bargain considering the paintwork, chrome etc would (hopefully) be to a higher standard than the original although Honda finish was always a strong point.
A modern day Honda CB500X retails for £6,069.