Databases range in size from simple books made searchable, to several billion records in the larger news databases. The retail database industry is obscure.
Costs are highly variable and difficult to determine in advance.
Products with the same name may contain different information. An individual magazine or database may exist within several databases and several collections. Within this confusion are the definitive, must-search databases. Definitive databases are determined by success in the market. Not necessarily the 'best', nor most useful but the market-successful become definitive resources over time.