Cheap sources are trees, or bags you'd find at a hardware store or garden center. I paid about 5 euros for 20 liters of pine bark chips. In some places, pet stores have the good stuff as well.
You generally would want conifer wood, so pine can be good, but fir and cedar seem to work well too! Do not fall for beech chips (waste from vinegar production) because they suck, but they're darn cheap, five to six times cheaper than pine bark. Those have the life sucked out of them and they act as a problematic soil compound that you'd want to avoid.
Succulents hardly make wood, but I believe some of them are grown in pine wood chips just like some orchids are.. Those chips are usually pretty expensive compared to your run of the mill stuff you can get at pet stores or hardware stores and nobody knows why, except the guys selling it with a 400% mockup. The pet store stuff is sometimes sterilized with gamma radiation, which isn't harmful to you or your plants (unless you stand in front of the radiation source, don't gamma sterilize at home), so it will be less biologically active at the start. Grab some forest soil and dump it in the bag, wet it, and forget about it for a couple weeks. Should be back to normal.
If you're going to buy it online, make sure you don't pick the dyed bark flakes, because that paint is going to be a paint in the ass. I've read about a couple people making that mistake, who are now left with cubic tons of the stuff.