Does black primer exist outside of hobby shops?
There are some colours where you have to have em, and they do make great paint, but for primers and for varnishes/coatings etc there is no reason to go with Citadel. Some people say generic flat-black or matt-black isn’t as dark black as Citadels, but I have never noticed a problem. There is a strong suspiscion in “the community” that GW paints are rebranded from regular paints, and that the regular paint in question is “Hycote” car spray. See if you can get your hands on that, at a tenth of the price. Sources: My geek skills!