A decent Kamaka 'ukulele starts at around $500 US and can run $1000 US for a tenor, so £400 not high for a really good instrument. An Eckhaus runs $600-800. Hohners run $300 plus. Can't find 'Hathaway," however, so sounds like the seller is fishing for top dollar on an unknown.
For good ones see See Kamaka 'ukulele

A local music store suggested that one of the string players named Hathaway might have had an instrument built for him, but this seems doubtful. Nothing in their catalogues about Hathaway 'ukulele or other stringed instruments.

A Terry Hathaway had a musical instrument store in California about 25 years ago, but can't connect stringed instruments to him.