If you are in usa then after the 50 you start paying listing fees. So I suggest you check with your country's listing fees cost and multiply until you reach the monthly store's cost. This number should be when it's cost efficient to get a basic store. But since store has perks like good til cancelled, maybe you wanna get it earlier.
I also suggest you make a plan on listing fast for the next days, so you quickly fill your new store's 250 empty free "shelves"
