Chuck's rule of thumb: If the component cost is less than $10, but
several of them. In other words, if you need a 10uF 15v electrolytic,
buy 10 of them.
My parts drawers overfloweth.
I do a similar thing, but based on usefulness rather than price. If I was
buying a small mains transformer it may well cost < \pounds 10.00
but I would probably only buy one or two. But for an expensive but
useful IC I might well buy at least 5.
For really common parts (LEDs, resistors, decoupling caps,
IC sockets, etc) I often go to the quantity to get the first discount
price (often 50 or 100). I use them enough..
My parts _rooms_ overfloweth :-)
-tony