The details of what an eBay store subscription means have changed substantially over the recent few years. A number of changes have been made at different times, and I don't have a detailed chronology of it, but...

At one point in time, a seller without a store subscription had access to two "formats" - (1) Auction and (2) Fixed Price. Each format could have a duration as long as 10 days. For the purposes of exposure in eBay search, those were considered to be "core" items, and could be found using the regular default search. Both of those formats had insertion fees that were based on the minimum price for which the item could be sold; the higher that price, the higher the cost to "go fishing".

A seller with a store subscription had access to an additional format - Store Inventory Format. The insertion fee was a flat $0.05 per item per 30 days. Items listed as Store Inventory Format were not considered to be "core" items, and could not be found using the regular default search. In order to see store items in a search, a prospective buyer had to specify that option in the search. As a matter of strategy, store operators often included some Auction and/or Fixed Price items in their mix of listings in the hope of having prospective buyers "find" their store through the search exposure those formats received.

Today, many things are different than they were at the point in time described above.

Auction format - aside from the "free 50" - still has insertion fees that depend upon the minimum price for which the item can be sold.

Fixed Price format now has a flat insertion fee, and can have a duration as long as 30 days. For those without a store subscription, the basic insertion fee is $0.50, regardless of item price.

Store Inventory Format no longer exists. Yes, listings will show up "in a store" if one looks at that store, but they are all regular Fixed Price listings, available through the regular default search. For Fixed Price items, sellers with store subscriptions have discounted insertion fees compared to those without - either $0.20, $0.05, or $0.03 per item per 30 days, depending on the type of store subscription.