Also sometimes the cheap consumable is a false economy. If the $40 chain lasts twice as long as the $30 chain, then the more expensive part is the better buy. This explains why I replaced the worn out SRAM 951 chain on my commuter with a Shimano XTR chain. I also find that more expensive tires hold up better and Jagwire cables are worth the premium over generic just because they are less hassle to set up.
I buy mostly mid range bikes and usually end up with mid-range replacement parts since I usually buy equivalent or better, so worn out LX/105 cassettes mostly end up replaced with XT/Ultegra and rim brake pads are mostly replaced with KoolStop.