Usually Newegg and Amazon, sometimes NextWarehouse for things I’m not in a rush for (they do a lot of drop shipping from the distributors/manufactures themselves so it’s sometimes cheaper but also slower). B&H is also worth a look, sometimes they do price drops on things & end up being cheaper than the other places.
There’s a local Best Buy near me that’s in a special tax district (lower sales tax) so I could try checking them out but usually the prices there are marked up so much that it’s not worth it IMO.
There aren’t any Micro Centers near me, it’d take a fair amount of travel to get to one.