I think your estimate of £100 for 28 hole DA7600 is way off.
These are only available as Japanese import and usually about £250 before shipping and duty etc.
Curious to know why you value the rims at £300 too?.....
Dollars or pounds; I’d say it’s a fair price.
~100 quid worth of hubs and ~300 quid worth of rims. Yeah its very overpriced.