Glass canning jars are absolutely ridiculous here in Belgium. I garden and I am going to scale up my gardening next year, so I need to get into canning and preserving again.
If you live in the US, you could get a 12 pack of standard mason jars in a store for https://www.target.com/p/ball-16oz-12pk-glass-regular-mouth-mason-jar-with-lid-and-band/-/A-12794405 under $15.
Here, any sort of glass jar is no cheaper than 20€ for 6 online and in stores it is often 5-10€ per jar, depending on size!! That is 300% more expensive on the cheap end here. It is not super sustainable to have to spend 200 euros on glass jars to can your extra fruit and vegetables.
Is there a secret to finding reasonably-priced glass canning jars that some people have found? I would reuse glass jars that I get from the store, but you are not supposed to reuse the lids because they degrade and will let in harmful bacteria and let things oxidize.
I guess it is because of transportation cost and economy of scales - moving empty jars around is the same amount of space and thus the cost of warehousing and shipping is probably quite similar and at the same time these factories can buy them by the shipping container and you have to pay all the intermediate sellers too. Also the vat you pay is roughly similar since the empty jar is as expensive as the filled jar. My advice (based more on budget friendlyness than sustainability) would be to find a brand that sells something you cannot grow but do like to eat and then buy a bunch of those in the same size.
Also maybe put up a note at work or the Albert Heijn statingthat you are looking for (unbranded) mason jars because of your love for gardening and who knows you might get in touch with someone like-minded or very lonely who happens to have a bunch of spares.