It depends on what your goal is. Quantity = low price as Gordon say. Howeverif you want to perform a good clean to a PC this includes the internals - you would be looking at about £3 - 5 per pc. Telephones from £0.55p photocopiers £1 - 3 quid.
You can either do a in a clean for a mini or a clean for an Aston Martin - there is a huge difference. Put it like this after most firms I know. I say this I will show you the difference after THEY have cleaned the equipment I will re-clean it and I let the customer decide. I have always got the work after these tests. Good work speaks for itself
Dave