I have been buying dozens of small items mostly from ebay and I have found a few things are frustratingly expensive. Not to mention the risk of utter tosh which is either barely fit for purpose or just completely unfit for purpose.
Then I started to notice a few things. I knew these already, but it was a nice reminder. In particular be prepared to look outside your domain. A item sold in one domain, say "hobby electronics" can have a significantly (orders of magnitude) different price point than the exact same item sold in a different domain.
Consider wire. I was looking for some sensible, multi-stranded wire gauge for the 1A-5A range which basic Dupoint jumpers etc. don't really do. When I search on ebay there are dozens and dozens of people selling various gauges of wire in 1 meter length for the likes of £0.99
However, while pricing a project (Infinity Mirror table top), I found a link to speaker cable in the gauges I needed. Instead of £1 a meter this stuff was being sold by the REEL for £6. £6 for 150 meters of the stuff.
You will see this a lot. Another example I remember seeing was a waterproof sat nav bracket for a motorcycle. In Halfords it was priced at £45. However two shelves over they were selling the EXACT same item for bicycles for £15. This is all to do with PPP Product, Price, Placement. The marketing scum believe/know that someone shopping for a bracket for a motorcycle will expect to pay more than one shopping for a bicycle.
So always consider other domains within which the item you are looking for might exist.
In the case of wire. A hobby electronics person might only be considering a meter or two length, so paying £1 or £2 seems okay. A person wiring their living room with speakers might be considering 10 or 20 meter lengths and paying £10 or £20 would not seem so good. It's EXACTLY the same cable.
Another thing I spotted, which is quite clever on the ebay seller's part and foolish on the buyer is ebay breadboards. Because ebay breadboards are 99% Chinese fakes or no-name boards at least one seller has taken to buying branded breadboards and listing them at a premium price.
Consider these - Genuine (I assume) Twin Industries branded breadboard.
https://www.ebay.co.uk/itm/TWIN-INDUSTRIES-TW-E41-1020-BREADBOARD-SOLDERLESS-830-TIE-POINTS/182121558017?epid=1050989681&hash=item2a674a7001:g:B0YAAOSwiYFXLM88Of course these are fully branded premium breadboards you would expect to pay a bit more, right?
Well, they are £8+VAT on CPC and £8.50+VAT on Element14.
This seller is making a killing buying them no doubt in bulk from CPC and relisting them on ebay for 2 to 3 times the price! Praying on people's fear of cheap breadboards. I have also seen sellers listing the same exact breadboard at 10 different prices, ranging from £3 to £30!
Another example would be DC plugs and sockets. Bought individually from a hobby electronics store or ebay seller they can be £1-2 each or higher. However if you look into the LED lighting domain on Amazon they sell them in packs of 10 or 20 for £5-£10. Half the price! The same can be said for various 12V PSUs, wall warts and fittings.
Clearly it pays to shop around and think outside your domain.