Niagen owns the patent, and hasn’t licensed manufacture, so any vendor buys it from them. Markups vary, so cheapest brand varies. No generics.
Niacinamide and 5-HTP are precursors and much cheaper, but no research to demonstrate effectiveness.
Niacinamide/NM, Niacinamide Riboside/NR and nicotinic acid/Niacin are all a little bit different. Niagen is a patented NR and claims to be a better precursor for NAD+ than NM. Who knows? I do take the Niagen version, which is in a couple of products including True Niagen. I predict you will see many products, like skin care, stating NAD+ properties. Remember the Coconut Oil craze??? Personally, believe the NAD+ oral supplements have potential. Dubious about the others.