PS1 classics are now available for purchase in the catalogue, as well as PlayStation Plus Premium, so you may add them to your library without having to connect to the service.
Therefore, there is always doubt about the existence or absence of individual classic games as items that may be purchased on the PlayStation Store in the most recent cases, although the option is confirmed. Each of the four classic games included today in the catalog may be purchased separately.
Further, you may see the individual titles' prices as well as their prices on the following links:
All people are entitled to PS1 backwards compatibility games, regardless of whether or not they have a subscription. For the rest, we have seen the new PlayStation Plus Extra and Premium PS5 and PS4 games announced a few days ago and available starting today, among which the presence of Horizon Forbidden West stands out.