Typical rip off, cold climate fluid for the power steering, LR wanted over 22 quid for a half litre, you can get exactly the same stuff on the bay for around £16. Still expensive though.
Fluids and filters, from wherever is cheapest. If you change them regularly you shouldn't have trouble.
For parts, I do look at the recommended sellers on the bay, most of them do sell on there, but if the parts aren't available on there, I'll usually google the part number, if I have it and see what suppliers pop up.
I only use local motor factors or Halfrauds if I really need the part urgently.