Buying components should, in my experience as a hobbyist only be done for mature projects which are reliable or projects where the needed spec or type just cant be made or found.
Here are some tricks that have served me well and other young hobbyist may benefit from :
First, assess what your building now and might be in the future. Go from there. For instance if your building power supplies look for computer PS’s in the dumpster or from family or friends. If your into tiny robotics look at DVD players and motorized toys for the small motors and mechanics inside.
Many of your ideas will fail for the few that will end up working, don’t fear that. Buy spec’ed components only for those projects that make it.
Second, some examples :
ATX power supplies.
More ATX parts
ATX parts
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ATX psu cases. These are great for your reinvented power supplies or any other project such as an Arduino based device.
Ferrite SMPS trasnsformer as seen after desoldering.
Inductors, these are some of the most expensive of all components and nearly impossible for the average person to have made buy a company. The Cores can easily be stripped of their existing coils and wound to your own needs.