md0u80c9: Acorn profited from selling complete solutions, Apple profited from selling complete solutions (witness the rapid death of the "clone" Mac manufacturer policy), why should Castle be different?
I'm not sure what you mean by "part-exchanged mobos cost £600". Who part-exchanged a motherboard with whom, for that price? What sort of motherboard was it?
When you talk about £600 for "the remaining components", what do you think Castle are charging for the operating system? Or for Oregano 2? Or for the other bundled applications?
Are you planning to sell a post-Risc PC RISC OS computer yourself? Oh, wait, MicroDigital do that already