Specification Creep

In our case it means we're creeping oh-so-slowly towards a specification... How on earth do you decide how much (how little!) you need to spend on eg a thermostatic shower unit? £300? £500? £1000? I can find the same size shower screen for anything from £96 to £576. Why on earth does a 900x300x600mm unit which is just a box of MDF without even a top surface appear to cost £504? And where on earth do you go to get impartial advice? I am ploughing my way round the various suppliers and showrooms seeing whether any of the advice overlaps. Today is lay-out-the-utility-room day. But the view from the window this morning reminds me why we're doing it: