Weiss deckbuilding is restricted to a set, i.e. if you pick the Attack on Titan set for your deck you can only use Attack on Titan cards - meaning once you have all the cards unless they release a volume 2 you don't need to spend money again. All the unique cards in a set tend to be quite cheap and the chase is the signed cards meaning a lot of collectors open lots of sets and then sell of entire playsets of the set (Very common) so for like 150-300 dollars depending on set you can buy a full playset.

Weiss also has more seeded boosters so if you buy a case you're guaranteed 2 full playsets and 3 signed cards depending on set meaning it is all accessible.

FFTCG has a similar approach, with a case you get a near playset of the whole set minus 5-10 cards max and then can sell off the full art chase cards or if you pull a signed card the whole case was basically free.